Application language now can be changed in the settings

android-app/proguard.cfg

@@ -95,6 +95,10 @@
     public static int e(...);
 }
 
+-assumenosideeffects class org.solovyev.android.Check {
+    *;
+}
+
 #
 #*********************************************************************
 #

android-app/src/main/java/org/solovyev/android/Check.java

@@ -0,0 +1,166 @@
+/*
+ * Copyright 2014 serso aka se.solovyev
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ * Contact details
+ *
+ * Email: se.solovyev@gmail.com
+ * Site:  http://se.solovyev.org
+ */
+
+package org.solovyev.android;
+
+import android.os.Looper;
+
+import java.util.Collection;
+import java.util.Map;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+import static java.lang.Thread.currentThread;
+
+public final class Check {
+
+	private static final boolean junit = isJunit();
+
+	private static boolean isJunit() {
+		final StackTraceElement[] stackTrace = currentThread().getStackTrace();
+		for (StackTraceElement element : stackTrace) {
+			if (element.getClassName().startsWith("org.junit.")) {
+				return true;
+			}
+		}
+		return false;
+	}
+
+	private Check() {
+		throw new AssertionError();
+	}
+
+	public static void isMainThread() {
+		if (!junit && Looper.getMainLooper() != Looper.myLooper()) {
+			throw new AssertionException("Should be called on the main thread");
+		}
+	}
+
+	public static void isNotNull(@Nullable Object o) {
+		isNotNull(o, "Object should not be null");
+	}
+
+	public static void isNotNull(@Nullable Object o, @Nonnull String message) {
+		if (o == null) {
+			throw new AssertionException(message);
+		}
+	}
+
+	public static void notEquals(int expected, int actual) {
+		if (expected == actual) {
+			throw new AssertionException("Should not be equal");
+		}
+	}
+
+	public static void equals(int expected, int actual) {
+		if (expected != actual) {
+			throw new AssertionException("Should be equal");
+		}
+	}
+
+	public static void equals(@Nullable Object expected, @Nullable Object actual) {
+		equals(expected, actual, "Should be equal");
+	}
+
+	public static void equals(@Nullable Object expected, @Nullable Object actual, @Nonnull String message) {
+		if (expected == actual) {
+			// both nulls or same
+			return;
+		}
+
+		if (expected != null && actual != null && expected.equals(actual)) {
+			// equals
+			return;
+		}
+
+		throw new AssertionException(message);
+	}
+
+	public static void isTrue(boolean expression, @Nonnull String message) {
+		if (!expression) {
+			throw new AssertionException(message);
+		}
+	}
+
+	public static void isFalse(boolean expression, @Nonnull String message) {
+		if (expression) {
+			throw new AssertionException(message);
+		}
+	}
+
+	public static void isNull(@Nullable Object o) {
+		isNull(o, "Object should be null");
+	}
+
+	public static void isNull(@Nullable Object o, @Nonnull String message) {
+		if (o != null) {
+			throw new AssertionException(message);
+		}
+	}
+
+	public static void isNotEmpty(@Nullable String s) {
+		if (s == null || s.length() == 0) {
+			throw new AssertionException("String should not be empty");
+		}
+	}
+
+	public static void isNotEmpty(@Nullable String[] array) {
+		if (array == null || array.length == 0) {
+			throw new AssertionException("Array should not be empty");
+		}
+	}
+
+	public static void isNotEmpty(@Nullable Collection<?> c) {
+		if (c == null || c.size() == 0) {
+			throw new AssertionException("Collection should not be empty");
+		}
+	}
+
+	public static void isNotEmpty(@Nullable Map<?, ?> c) {
+		if (c == null || c.size() == 0) {
+			throw new AssertionException("Map should not be empty");
+		}
+	}
+
+	public static void same(Object expected, Object actual) {
+		if (expected != actual) {
+			throw new AssertionException("Objects should be the same");
+		}
+	}
+
+	public static void isEmpty(@Nullable Collection<?> c) {
+		if (c != null && !c.isEmpty()) {
+			throw new AssertionException("Collection should be empty");
+		}
+	}
+
+	public static void shouldNotHappen() {
+		throw new AssertionException("Should not happen");
+	}
+
+	private static final class AssertionException extends RuntimeException {
+		private AssertionException(@Nonnull String message) {
+			super(message);
+		}
+	}
+}

android-app/src/main/java/org/solovyev/android/calculator/ActivityUi.java

@@ -38,8 +38,11 @@ import android.util.DisplayMetrics;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.TextView;
+
 import org.solovyev.android.Activities;
 import org.solovyev.android.Views;
+import org.solovyev.android.calculator.language.Language;
+import org.solovyev.android.calculator.language.Languages;
 import org.solovyev.android.sherlock.tabs.ActionBarFragmentTabListener;
 
 import javax.annotation.Nonnull;
@@ -50,10 +53,13 @@ public class ActivityUi extends BaseUi {
 	private int layoutId;
 
 	@Nonnull
-	private Preferences.Gui.Theme theme;
+	private Preferences.Gui.Theme theme = Preferences.Gui.Theme.default_theme;
 
 	@Nonnull
-	private Preferences.Gui.Layout layout;
+	private Preferences.Gui.Layout layout = Preferences.Gui.Layout.main_calculator;
+
+	@Nonnull
+	private Language language = Languages.SYSTEM_LANGUAGE;
 
 	private int selectedNavigationIndex = 0;
 
@@ -73,11 +79,13 @@ public class ActivityUi extends BaseUi {
 		activity.setTheme(theme.getThemeId(activity));
 
 		layout = Preferences.Gui.getLayout(preferences);
+		language = App.getLanguages().getCurrent();
 	}
 
 	@Override
 	public void onCreate(@Nonnull Activity activity) {
 		super.onCreate(activity);
+		App.getLanguages().updateLanguage(activity, false);
 
 		if (activity instanceof CalculatorEventListener) {
 			Locator.getInstance().getCalculator().addCalculatorEventListener((CalculatorEventListener) activity);
@@ -146,16 +154,29 @@ public class ActivityUi extends BaseUi {
 	}
 
 	public void onResume(@Nonnull Activity activity) {
-		restartIfThemeChanged(activity, theme);
+		if (!restartIfThemeChanged(activity, theme)) {
+			restartIfLanguageChanged(activity, language);
+		}
 	}
 
-	public static void restartIfThemeChanged(@Nonnull Activity activity, @Nonnull Preferences.Gui.Theme oldTheme) {
+	public static boolean restartIfThemeChanged(@Nonnull Activity activity, @Nonnull Preferences.Gui.Theme oldTheme) {
 		final Preferences.Gui.Theme newTheme = Preferences.Gui.theme.getPreference(App.getPreferences());
 		final int themeId = oldTheme.getThemeId(activity);
 		final int newThemeId = newTheme.getThemeId(activity);
 		if (themeId != newThemeId) {
 			Activities.restartActivity(activity);
+			return true;
 		}
+		return false;
+	}
+
+	public static boolean restartIfLanguageChanged(@Nonnull Activity activity, @Nonnull Language oldLanguage) {
+		final Language current = App.getLanguages().getCurrent();
+		if (!current.equals(oldLanguage)) {
+			Activities.restartActivity(activity);
+			return true;
+		}
+		return false;
 	}
 
 	public void onPause(@Nonnull Activity activity) {
@@ -254,6 +275,11 @@ public class ActivityUi extends BaseUi {
 		return theme;
 	}
 
+	@Nonnull
+	public Language getLanguage() {
+		return language;
+	}
+
 	@Nonnull
 	public Preferences.Gui.Layout getLayout() {
 		return layout;

android-app/src/main/java/org/solovyev/android/calculator/App.java

@@ -39,6 +39,7 @@ import org.solovyev.android.Android;
 import org.solovyev.android.UiThreadExecutor;
 import org.solovyev.android.Views;
 import org.solovyev.android.calculator.ga.Ga;
+import org.solovyev.android.calculator.language.Languages;
 import org.solovyev.android.calculator.view.ScreenMetrics;
 import org.solovyev.android.calculator.widget.BaseCalculatorWidgetProvider;
 import org.solovyev.android.calculator.widget.CalculatorWidgetProvider;
@@ -117,6 +118,9 @@ public final class App {
 	@Nonnull
 	private static volatile ScreenMetrics screenMetrics;
 
+	@Nonnull
+	private static final Languages languages = new Languages();
+
 	private App() {
 		throw new AssertionError();
 	}
@@ -177,6 +181,7 @@ public final class App {
 					Android.enableComponent(application, CalculatorWidgetProvider4x4.class, false);
 				}
 			}
+			App.languages.init(App.preferences);
 
 			App.initialized = true;
 		} else {
@@ -277,6 +282,11 @@ public final class App {
 		return Preferences.Gui.getTheme(getPreferences());
 	}
 
+	@Nonnull
+	public static Languages getLanguages() {
+		return languages;
+	}
+
 	public static boolean isLg() {
 		if (lg == null) {
 			lg = "lge".equalsIgnoreCase(Build.BRAND) || "lge".equalsIgnoreCase(Build.MANUFACTURER);

android-app/src/main/java/org/solovyev/android/calculator/CalculatorApplication.java

@@ -37,6 +37,7 @@ import org.acra.ReportingInteractionMode;
 import org.acra.annotation.ReportsCrashes;
 import org.solovyev.android.Android;
 import org.solovyev.android.calculator.history.AndroidCalculatorHistory;
+import org.solovyev.android.calculator.language.Language;
 import org.solovyev.android.calculator.model.AndroidCalculatorEngine;
 import org.solovyev.android.calculator.onscreen.CalculatorOnscreenStartActivity;
 import org.solovyev.android.calculator.plot.AndroidCalculatorPlotter;
@@ -48,6 +49,7 @@ import org.solovyev.common.msg.MessageType;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.concurrent.TimeUnit;
 
 import javax.annotation.Nonnull;
@@ -139,8 +141,10 @@ public class CalculatorApplication extends android.app.Application implements Sh
 		preferences.registerOnSharedPreferenceChangeListener(this);
 
 		setTheme(preferences);
+		setLanguageInitially();
 
 		super.onCreate();
+		App.getLanguages().updateLanguage(this, true);
 
 		if (!Preferences.Ga.initialReportDone.getPreference(preferences)) {
 			App.getGa().reportInitially(preferences);
@@ -199,6 +203,14 @@ public class CalculatorApplication extends android.app.Application implements Sh
 		}, 100, TimeUnit.MILLISECONDS);
 	}
 
+	private void setLanguageInitially() {
+		// should be called before onCreate()
+		final Language language = App.getLanguages().getCurrent();
+		if (!language.isSystem() && !language.locale.equals(Locale.getDefault())) {
+			Locale.setDefault(language.locale);
+		}
+	}
+
 	private void setTheme(@Nonnull SharedPreferences preferences) {
 		final Preferences.Gui.Theme theme = Preferences.Gui.getTheme(preferences);
 		setTheme(theme.getThemeId());

android-app/src/main/java/org/solovyev/android/calculator/Preferences.java

@@ -29,19 +29,28 @@ import android.graphics.Color;
 import android.support.annotation.StyleRes;
 import android.util.SparseArray;
 import android.view.ContextThemeWrapper;
-import jscl.AngleUnit;
+
-import jscl.NumeralBase;
+import org.solovyev.android.calculator.language.Languages;
 import org.solovyev.android.calculator.math.MathType;
 import org.solovyev.android.calculator.model.AndroidCalculatorEngine;
 import org.solovyev.android.calculator.onscreen.CalculatorOnscreenService;
 import org.solovyev.android.calculator.preferences.PurchaseDialogActivity;
 import org.solovyev.android.calculator.wizard.WizardActivity;
-import org.solovyev.android.prefs.*;
+import org.solovyev.android.prefs.BooleanPreference;
+import org.solovyev.android.prefs.IntegerPreference;
+import org.solovyev.android.prefs.LongPreference;
+import org.solovyev.android.prefs.NumberToStringPreference;
+import org.solovyev.android.prefs.Preference;
+import org.solovyev.android.prefs.StringPreference;
+
+import java.text.DecimalFormatSymbols;
+import java.util.Locale;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
-import java.text.DecimalFormatSymbols;
+
-import java.util.Locale;
+import jscl.AngleUnit;
+import jscl.NumeralBase;
 
 import static org.solovyev.android.Android.isPhoneModel;
 import static org.solovyev.android.DeviceModel.samsung_galaxy_s;
@@ -80,8 +89,8 @@ public final class Preferences {
 
 		public static final Preference<Theme> theme = StringPreference.ofEnum("org.solovyev.android.calculator.CalculatorActivity_calc_theme", Theme.material_theme, Theme.class);
 		public static final Preference<Layout> layout = StringPreference.ofEnum("org.solovyev.android.calculator.CalculatorActivity_calc_layout", Layout.simple, Layout.class);
+		public static final Preference<String> language = StringPreference.of("gui.language", Languages.SYSTEM_LANGUAGE_CODE);
 		public static final Preference<Boolean> feedbackWindowShown = BooleanPreference.of("feedback_window_shown", false);
-		public static final Preference<Boolean> notesppAnnounceShown = BooleanPreference.of("notespp_announce_shown", false);
 		public static final Preference<Boolean> showReleaseNotes = BooleanPreference.of("org.solovyev.android.calculator.CalculatorActivity_show_release_notes", true);
 		public static final Preference<Boolean> usePrevAsBack = BooleanPreference.of("org.solovyev.android.calculator.CalculatorActivity_use_back_button_as_prev", false);
 		public static final Preference<Boolean> showEqualsButton = BooleanPreference.of("showEqualsButton", true);
@@ -264,13 +273,13 @@ public final class Preferences {
 			Gui.layout.putDefault(preferences);
 		}
 		applyDefaultPreference(preferences, Gui.feedbackWindowShown);
-		applyDefaultPreference(preferences, Gui.notesppAnnounceShown);
 		applyDefaultPreference(preferences, Gui.showReleaseNotes);
 		applyDefaultPreference(preferences, Gui.usePrevAsBack);
 		applyDefaultPreference(preferences, Gui.showEqualsButton);
 		applyDefaultPreference(preferences, Gui.autoOrientation);
 		applyDefaultPreference(preferences, Gui.hideNumeralBaseDigits);
 		applyDefaultPreference(preferences, Gui.preventScreenFromFading);
+		applyDefaultPreference(preferences, Gui.language);
 
 		applyDefaultPreference(preferences, Graph.plotImag);
 		applyDefaultPreference(preferences, History.showIntermediateCalculations);

android-app/src/main/java/org/solovyev/android/calculator/language/Language.java

@@ -0,0 +1,69 @@
+package org.solovyev.android.calculator.language;
+
+import android.content.Context;
+import android.text.TextUtils;
+
+import org.solovyev.android.calculator.R;
+
+import java.util.Locale;
+
+import javax.annotation.Nonnull;
+
+public final class Language {
+	@Nonnull
+	public final String code;
+
+	@Nonnull
+	public final Locale locale;
+
+	@Nonnull
+	final String name;
+
+	public Language(@Nonnull String code, @Nonnull Locale locale) {
+		this.code = code;
+		this.locale = locale;
+		this.name = makeName(code, locale);
+	}
+
+	@Nonnull
+	public String getName(@Nonnull Context context) {
+		if (!isSystem()) {
+			return name;
+		} else {
+			return context.getString(R.string.cpp_system_language) + " (" + locale.getDisplayLanguage(locale) + ")";
+		}
+	}
+
+	@Nonnull
+	private static String makeName(@Nonnull String code, @Nonnull Locale locale) {
+		if (code.equals(Languages.SYSTEM_LANGUAGE_CODE)) {
+			return "";
+		}
+
+		final int underscore = code.indexOf("_");
+		if (underscore >= 0 && TextUtils.isEmpty(locale.getDisplayCountry(locale))) {
+			return locale.getDisplayName(locale) + " (" + code.substring(underscore + 1) + ")";
+		}
+
+		return locale.getDisplayName(locale);
+	}
+
+	public boolean isSystem() {
+		return code.equals(Languages.SYSTEM_LANGUAGE_CODE);
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (this == o) return true;
+		if (o == null || getClass() != o.getClass()) return false;
+
+		final Language language = (Language) o;
+		return code.equals(language.code);
+
+	}
+
+	@Override
+	public int hashCode() {
+		return code.hashCode();
+	}
+}

android-app/src/main/java/org/solovyev/android/calculator/language/Languages.java

@@ -0,0 +1,168 @@
+package org.solovyev.android.calculator.language;
+
+import android.content.Context;
+import android.content.SharedPreferences;
+import android.content.res.Configuration;
+import android.content.res.Resources;
+import android.text.TextUtils;
+import android.util.DisplayMetrics;
+import android.util.Log;
+
+import org.solovyev.android.Check;
+import org.solovyev.android.calculator.App;
+import org.solovyev.android.calculator.Preferences;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.List;
+import java.util.Locale;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
+public final class Languages implements SharedPreferences.OnSharedPreferenceChangeListener {
+
+	@Nonnull
+	private static final Locale[] locales = Locale.getAvailableLocales();
+	@Nonnull
+	public static final String SYSTEM_LANGUAGE_CODE = "00";
+	@Nonnull
+	public static final Language SYSTEM_LANGUAGE = new Language(SYSTEM_LANGUAGE_CODE, Locale.getDefault());
+	@Nonnull
+	private final List<Language> list = new ArrayList<>();
+
+	public void init(@Nonnull SharedPreferences preferences) {
+		preferences.registerOnSharedPreferenceChangeListener(this);
+	}
+
+	@Nonnull
+	public List<Language> getList() {
+		Check.isMainThread();
+		if (list.isEmpty()) {
+			loadList();
+		}
+		return list;
+	}
+
+	private void loadList() {
+		Check.isMainThread();
+		Check.isEmpty(list);
+		tryAddLanguage("ar");
+		tryAddLanguage("cs");
+		tryAddLanguage("en");
+		tryAddLanguage("es_ES");
+		tryAddLanguage("de");
+		tryAddLanguage("fi");
+		tryAddLanguage("fr");
+		tryAddLanguage("it");
+		tryAddLanguage("it");
+		tryAddLanguage("pl");
+		tryAddLanguage("pt_BR");
+		tryAddLanguage("pt_PT");
+		tryAddLanguage("ru");
+		tryAddLanguage("vi");
+		tryAddLanguage("uk");
+		tryAddLanguage("ja");
+		tryAddLanguage("zh_CN");
+		tryAddLanguage("zh_TW");
+		Collections.sort(list, new Comparator<Language>() {
+			@Override
+			public int compare(Language lhs, Language rhs) {
+				return lhs.name.compareTo(rhs.name);
+			}
+		});
+		list.add(0, SYSTEM_LANGUAGE);
+	}
+
+	private void tryAddLanguage(@Nonnull String locale) {
+		final Language language = makeLanguage(locale);
+		if (language != null) {
+			list.add(language);
+		}
+	}
+
+	@Nullable
+	private static Language makeLanguage(@Nonnull String localeId) {
+		final Locale locale = findLocaleById(localeId);
+		if (locale == null) {
+			return null;
+		}
+		return new Language(localeId, locale);
+	}
+
+	@Nullable
+	private static Locale findLocaleById(@Nonnull String id) {
+		for (Locale locale : locales) {
+			if (TextUtils.equals(locale.toString(), id)) {
+				return locale;
+			}
+		}
+
+		final String language;
+		final int underscore = id.indexOf("_");
+		if (underscore >= 0) {
+			language = id.substring(0, underscore);
+		} else {
+			language = id;
+		}
+
+		for (Locale locale : locales) {
+			if (TextUtils.equals(locale.getLanguage(), language)) {
+				return locale;
+			}
+		}
+
+		Log.d("Languages", "No locale found for " + id);
+		return null;
+	}
+
+	@Nonnull
+	public Language getCurrent() {
+		return get(Preferences.Gui.language.getPreference(App.getPreferences()));
+	}
+
+	@Nonnull
+	public Language get(@Nonnull String code) {
+		Language language = findLanguageByCode(code);
+		if (language != null) {
+			return language;
+		}
+		return SYSTEM_LANGUAGE;
+	}
+
+	@Nullable
+	private Language findLanguageByCode(@Nonnull String code) {
+		for (Language language : getList()) {
+			if (TextUtils.equals(language.code, code)) {
+				return language;
+			}
+		}
+		return null;
+	}
+
+	@Override
+	public void onSharedPreferenceChanged(@Nonnull SharedPreferences p, String key) {
+		if (Preferences.Gui.language.isSameKey(key)) {
+			updateLanguage(App.getApplication(), false);
+		}
+	}
+
+	public void updateLanguage(@Nonnull Context context, boolean initial) {
+		final Language language = getCurrent();
+		// we don't need to set system language while starting up the app
+		if (!initial || !language.isSystem()) {
+			if (!Locale.getDefault().equals(language.locale)) {
+				Locale.setDefault(language.locale);
+			}
+
+			final Resources r = context.getResources();
+			final DisplayMetrics dm = r.getDisplayMetrics();
+			final Configuration c = r.getConfiguration();
+			if (c.locale == null || !c.locale.equals(language.locale)) {
+				c.locale = language.locale;
+				r.updateConfiguration(c, dm);
+			}
+		}
+	}
+}

android-app/src/main/java/org/solovyev/android/calculator/preferences/PreferencesActivity.java

@@ -6,7 +6,6 @@ import android.content.SharedPreferences;
 import android.os.Bundle;
 import android.support.annotation.StringRes;
 import android.support.annotation.XmlRes;
-import android.text.TextUtils;
 import android.util.SparseArray;
 
 import org.solovyev.android.calculator.ActivityUi;
@@ -27,15 +26,27 @@ public class PreferencesActivity extends BaseActivity implements SharedPreferenc
 	static final String EXTRA_PREFERENCE_TITLE = "preference-title";
 
 	@Nonnull
-	private static final SparseArray<String> preferences = new SparseArray<>();
+	private static final SparseArray<PrefDef> preferences = new SparseArray<>();
 
 	static {
-		preferences.append(R.xml.preferences, "screen-main");
+		preferences.append(R.xml.preferences, new PrefDef("screen-main", R.string.c_app_settings));
-		preferences.append(R.xml.preferences_calculations, "screen-calculations");
+		preferences.append(R.xml.preferences_calculations, new PrefDef("screen-calculations", R.string.c_prefs_calculations_category));
-		preferences.append(R.xml.preferences_appearance, "screen-appearance");
+		preferences.append(R.xml.preferences_appearance, new PrefDef("screen-appearance", R.string.c_prefs_appearance_category));
-		preferences.append(R.xml.preferences_plot, "screen-plot");
+		preferences.append(R.xml.preferences_plot, new PrefDef("screen-plot", R.string.prefs_graph_screen_title));
-		preferences.append(R.xml.preferences_other, "screen-other");
+		preferences.append(R.xml.preferences_other, new PrefDef("screen-other", R.string.c_prefs_other_category));
-		preferences.append(R.xml.preferences_onscreen, "screen-onscreen");
+		preferences.append(R.xml.preferences_onscreen, new PrefDef("screen-onscreen", R.string.prefs_onscreen_title));
+	}
+
+	static class PrefDef {
+		@Nonnull
+		public final String id;
+		@StringRes
+		public final int title;
+
+		PrefDef(@Nonnull String id, int title) {
+			this.id = id;
+			this.title = title;
+		}
 	}
 
 	@Nonnull
@@ -53,8 +64,8 @@ public class PreferencesActivity extends BaseActivity implements SharedPreferenc
 		App.getPreferences().registerOnSharedPreferenceChangeListener(this);
 
 		final Intent intent = getIntent();
-		final String preferenceTitle = intent.getStringExtra(EXTRA_PREFERENCE_TITLE);
+		final int preferenceTitle = intent.getIntExtra(EXTRA_PREFERENCE_TITLE, 0);
-		if (!TextUtils.isEmpty(preferenceTitle)) {
+		if (preferenceTitle != 0) {
 			setTitle(preferenceTitle);
 		}
 
@@ -72,8 +83,12 @@ public class PreferencesActivity extends BaseActivity implements SharedPreferenc
 
 	@Override
 	public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
-		if (!paused && Preferences.Gui.theme.isSameKey(key)) {
+		if (!paused) {
+			if (Preferences.Gui.theme.isSameKey(key)) {
 				ActivityUi.restartIfThemeChanged(this, ui.getTheme());
+			} else if (Preferences.Gui.language.isSameKey(key)) {
+				ActivityUi.restartIfLanguageChanged(this, ui.getLanguage());
+			}
 		}
 	}
 
@@ -97,7 +112,7 @@ public class PreferencesActivity extends BaseActivity implements SharedPreferenc
 	}
 
 	@Nonnull
-	static SparseArray<String> getPreferences() {
+	static SparseArray<PrefDef> getPreferences() {
 		return preferences;
 	}
 
@@ -107,11 +122,11 @@ public class PreferencesActivity extends BaseActivity implements SharedPreferenc
 	}
 
 	@Nonnull
-	static Intent makeIntent(@Nonnull Context context, int preference, int title) {
+	static Intent makeIntent(@Nonnull Context context, @XmlRes int preference, @StringRes int title) {
 		final Intent intent = new Intent(context, PreferencesActivity.class);
 		intent.putExtra(EXTRA_PREFERENCE, preference);
 		if (title != 0) {
-			intent.putExtra(EXTRA_PREFERENCE_TITLE, context.getString(title));
+			intent.putExtra(EXTRA_PREFERENCE_TITLE, title);
 		}
 		return intent;
 	}

android-app/src/main/java/org/solovyev/android/calculator/preferences/PreferencesFragment.java

@@ -4,6 +4,7 @@ import android.content.Intent;
 import android.content.SharedPreferences;
 import android.os.Build;
 import android.os.Bundle;
+import android.preference.ListPreference;
 import android.preference.Preference;
 import android.util.SparseArray;
 import android.view.LayoutInflater;
@@ -13,12 +14,17 @@ import android.widget.ListView;
 import org.solovyev.android.calculator.AdView;
 import org.solovyev.android.calculator.App;
 import org.solovyev.android.calculator.CalculatorApplication;
+import org.solovyev.android.calculator.Preferences;
 import org.solovyev.android.calculator.R;
+import org.solovyev.android.calculator.language.Language;
+import org.solovyev.android.calculator.language.Languages;
 import org.solovyev.android.checkout.BillingRequests;
 import org.solovyev.android.checkout.Checkout;
 import org.solovyev.android.checkout.ProductTypes;
 import org.solovyev.android.checkout.RequestListener;
 
+import java.util.List;
+
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 
@@ -51,12 +57,12 @@ public class PreferencesFragment extends org.solovyev.android.material.preferenc
 		App.getPreferences().registerOnSharedPreferenceChangeListener(this);
 	}
 
-	private void setPreferenceIntent(int xml, @Nonnull String name) {
+	private void setPreferenceIntent(int xml, @Nonnull PreferencesActivity.PrefDef def) {
-		final Preference preference = findPreference(name);
+		final Preference preference = findPreference(def.id);
 		if (preference != null) {
 			final Intent intent = new Intent(getActivity(), PreferencesActivity.class);
 			intent.putExtra(PreferencesActivity.EXTRA_PREFERENCE, xml);
-			intent.putExtra(PreferencesActivity.EXTRA_PREFERENCE_TITLE, preference.getTitle());
+			intent.putExtra(PreferencesActivity.EXTRA_PREFERENCE_TITLE, def.title);
 			preference.setIntent(intent);
 		}
 	}
@@ -67,11 +73,11 @@ public class PreferencesFragment extends org.solovyev.android.material.preferenc
 
 		final int preference = getPreferencesResId();
 		if (preference == R.xml.preferences) {
-			final SparseArray<String> preferences = PreferencesActivity.getPreferences();
+			final SparseArray<PreferencesActivity.PrefDef> preferences = PreferencesActivity.getPreferences();
 			for (int i = 0; i < preferences.size(); i++) {
 				final int xml = preferences.keyAt(i);
-				final String name = preferences.valueAt(i);
+				final PreferencesActivity.PrefDef def = preferences.valueAt(i);
-				setPreferenceIntent(xml, name);
+				setPreferenceIntent(xml, def);
 			}
 			final Preference restartWizardPreference = findPreference("restart_wizard");
 			restartWizardPreference.setOnPreferenceClickListener(new Preference.OnPreferenceClickListener() {
@@ -96,6 +102,8 @@ public class PreferencesFragment extends org.solovyev.android.material.preferenc
 			}
 		}
 
+		prepareLanguagePreference(preference);
+
 		getCheckout().whenReady(new Checkout.ListenerAdapter() {
 			@Override
 			public void onReady(@Nonnull BillingRequests requests) {
@@ -121,6 +129,34 @@ public class PreferencesFragment extends org.solovyev.android.material.preferenc
 		onSharedPreferenceChanged(preferences, roundResult.getKey());
 	}
 
+	private void prepareLanguagePreference(int preference) {
+		if (preference != R.xml.preferences_appearance) {
+			return;
+		}
+
+		final ListPreference language = (ListPreference) preferenceManager.findPreference(Preferences.Gui.language.getKey());
+		final Languages languages = App.getLanguages();
+		final List<Language> languagesList = languages.getList();
+		final CharSequence[] entries = new CharSequence[languagesList.size()];
+		final CharSequence[] entryValues = new CharSequence[languagesList.size()];
+		for (int i = 0; i < languagesList.size(); i++) {
+			final Language l = languagesList.get(i);
+			entries[i] = l.getName(getActivity());
+			entryValues[i] = l.code;
+		}
+		language.setEntries(entries);
+		language.setEntryValues(entryValues);
+		language.setSummary(languages.getCurrent().getName(getActivity()));
+		language.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
+			@Override
+			public boolean onPreferenceChange(Preference preference, Object newValue) {
+				final Language l = languages.get((String) newValue);
+				language.setSummary(l.getName(getActivity()));
+				return true;
+			}
+		});
+	}
+
 	@Nonnull
 	private Checkout getCheckout() {
 		return ((PreferencesActivity) getActivity()).getCheckout();

android-app/src/main/java/org/solovyev/android/calculator/wizard/WizardActivity.java

@@ -8,9 +8,22 @@ import android.support.v4.app.Fragment;
 import android.support.v4.app.FragmentManager;
 import android.support.v4.app.FragmentStatePagerAdapter;
 import android.support.v4.view.ViewPager;
+
 import com.viewpagerindicator.PageIndicator;
-import org.solovyev.android.calculator.*;
+
-import org.solovyev.android.wizard.*;
+import org.solovyev.android.calculator.ActivityUi;
+import org.solovyev.android.calculator.App;
+import org.solovyev.android.calculator.BaseActivity;
+import org.solovyev.android.calculator.CalculatorApplication;
+import org.solovyev.android.calculator.Preferences;
+import org.solovyev.android.calculator.R;
+import org.solovyev.android.wizard.ListWizardFlow;
+import org.solovyev.android.wizard.Wizard;
+import org.solovyev.android.wizard.WizardFlow;
+import org.solovyev.android.wizard.WizardStep;
+import org.solovyev.android.wizard.WizardUi;
+import org.solovyev.android.wizard.Wizards;
+import org.solovyev.android.wizard.WizardsAware;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
@@ -190,6 +203,8 @@ public class WizardActivity extends BaseActivity implements WizardsAware, Shared
 	public void onSharedPreferenceChanged(SharedPreferences preferences, String key) {
 		if (Preferences.Gui.theme.isSameKey(key)) {
 			ActivityUi.restartIfThemeChanged(this, ui.getTheme());
+		} else if (Preferences.Gui.language.isSameKey(key)) {
+			ActivityUi.restartIfLanguageChanged(this, ui.getLanguage());
 		}
 	}
 

android-app/src/main/res/values/text_preferences.xml

@@ -7,9 +7,7 @@
 	<string name="c_show_equals_button_title">Show equals button</string>
 	<string name="c_show_equals_button_summary">If turned on equals button is shown</string>
 	<string name="c_hide_numeral_base_digits_title">Hide digits of other numeral systems</string>
-  <string name="c_hide_numeral_base_digits_summary">If turned on numeral base digits of other numeral bases will be
+	<string name="c_hide_numeral_base_digits_summary">If turned on numeral base digits of other numeral bases will be hidden</string>
-		hidden
-	</string>
 	<string name="prefs_history_show_intermediate_calculations_title">Show intermediate calculations in history</string>
 	<string name="prefs_history_show_intermediate_calculations_summary">If turned on all calculations will be shown in the
 		history screen
@@ -19,4 +17,5 @@
 	<string name="prefs_prevent_screen_from_fading_title">Prevent screen from fading</string>
 	<string name="prefs_prevent_screen_from_fading_summary">If turned on screen will not fade while using the app
 	</string>
+	<string name="prefs_language_title">Language</string>
 </resources>

android-app/src/main/res/values/text_strings.xml

@@ -231,4 +231,5 @@
   <string name="cpp_clear_history">Clear</string>
   <string name="cpp_new_in_version">New in %1$s version</string>
   <string name="cpp_release_notes_choose_theme">Do you want to try new Material themes? Choose them from the list:</string>
+  <string name="cpp_system_language">System language</string>
 </resources>

android-app/src/main/res/xml/preferences_appearance.xml

@@ -23,69 +23,74 @@
   -->
 
 <PreferenceScreen xmlns:a="http://schemas.android.com/apk/res/android"
-				  xmlns:range="http://schemas.android.com/apk/res-auto">
+				  xmlns:m="http://schemas.android.com/apk/res-auto">
+
+	<org.solovyev.android.material.preferences.ListPreference
+		a:key="gui.language"
+		a:title="@string/prefs_language_title"
+		m:materialColor="@color/material_text_selector"/>
 
 	<android.preference.CheckBoxPreference
+		a:defaultValue="true"
 		a:key="@string/p_calc_color_display_key"
 		a:summary="@string/c_calc_color_display_summary"
-				a:title="@string/c_calc_color_display_title"
+		a:title="@string/c_calc_color_display_title"/>
-				a:defaultValue="true"/>
 
 	<ListPreference
-				a:key="hapticFeedback"
-				a:title="@string/c_calc_haptic_feedback_title"
 		a:entries="@array/cpp_haptic_feedback_names"
+		a:entryValues="@array/cpp_haptic_feedback_values"
+		a:key="hapticFeedback"
 		a:summary="@string/c_calc_haptic_feedback_summary"
-				a:entryValues="@array/cpp_haptic_feedback_values"/>
+		a:title="@string/c_calc_haptic_feedback_title"/>
 
 	<ListPreference
-				a:key="@string/p_calc_multiplication_sign_key"
-				a:title="@string/c_calc_multiplication_sign"
 		a:entries="@array/p_multiplication_sign_values"
+		a:entryValues="@array/p_multiplication_sign_values"
+		a:key="@string/p_calc_multiplication_sign_key"
 		a:summary="@string/c_calc_multiplication_sign_summary"
-				a:entryValues="@array/p_multiplication_sign_values"/>
+		a:title="@string/c_calc_multiplication_sign"/>
 
 	<ListPreference
-				a:key="@string/p_calc_theme_key"
-				a:title="@string/c_calc_theme"
 		a:entries="@array/p_theme_names"
+		a:entryValues="@array/p_theme_values"
+		a:key="@string/p_calc_theme_key"
 		a:summary="@string/c_calc_theme_summary"
-				a:entryValues="@array/p_theme_values"/>
+		a:title="@string/c_calc_theme"/>
 
 	<ListPreference
-				a:key="@string/p_calc_layout_key"
-				a:title="@string/c_calc_layout"
 		a:entries="@array/p_layout_names"
+		a:entryValues="@array/p_layout_values"
+		a:key="@string/p_calc_layout_key"
 		a:summary="@string/c_calc_layout_summary"
-				a:entryValues="@array/p_layout_values"/>
+		a:title="@string/c_calc_layout"/>
 
 	<android.preference.CheckBoxPreference
+		a:defaultValue="true"
 		a:key="autoOrientation"
-				a:title="@string/c_auto_orientation_title"
 		a:summary="@string/c_auto_orientation_summary"
-				a:defaultValue="true"/>
+		a:title="@string/c_auto_orientation_title"/>
 
 
 	<android.preference.CheckBoxPreference
+		a:defaultValue="true"
 		a:key="showEqualsButton"
-				a:title="@string/c_show_equals_button_title"
 		a:summary="@string/c_show_equals_button_summary"
-				a:defaultValue="true"/>
+		a:title="@string/c_show_equals_button_title"/>
 
 	<android.preference.CheckBoxPreference
+		a:defaultValue="true"
 		a:key="hideNumeralBaseDigits"
-				a:title="@string/c_hide_numeral_base_digits_title"
 		a:summary="@string/c_hide_numeral_base_digits_summary"
-				a:defaultValue="true"/>
+		a:title="@string/c_hide_numeral_base_digits_title"/>
 
 	<android.preference.CheckBoxPreference
 		a:key="history_show_intermediate_calculations"
-				a:title="@string/prefs_history_show_intermediate_calculations_title"
+		a:summary="@string/prefs_history_show_intermediate_calculations_summary"
-				a:summary="@string/prefs_history_show_intermediate_calculations_summary"/>
+		a:title="@string/prefs_history_show_intermediate_calculations_title"/>
 
 	<android.preference.CheckBoxPreference
 		a:key="preventScreenFromFading"
-				a:title="@string/prefs_prevent_screen_from_fading_title"
+		a:summary="@string/prefs_prevent_screen_from_fading_summary"
-				a:summary="@string/prefs_prevent_screen_from_fading_summary"/>
+		a:title="@string/prefs_prevent_screen_from_fading_title"/>
 
 </PreferenceScreen>