Add preference to change app language (fixes #742)

src/main/AndroidManifest.xml

@@ -24,7 +24,8 @@
         android:theme="@style/Theme.Syncthing"
         android:description="@string/app_description"
         android:supportsRtl="true"
-        android:installLocation="internalOnly">
+        android:installLocation="internalOnly"
+        android:name=".SyncthingApp">
         <activity
                 android:name=".activities.FirstStartActivity"
                 android:label="@string/app_name">

src/main/java/com/nutomic/syncthingandroid/SyncthingApp.java

@@ -0,0 +1,14 @@
+package com.nutomic.syncthingandroid;
+
+import android.app.Application;
+
+import com.nutomic.syncthingandroid.util.Languages;
+
+public class SyncthingApp extends Application {
+
+    @Override
+    public void onCreate() {
+        super.onCreate();
+        new Languages(this).setLanguage(this);
+    }
+}

src/main/java/com/nutomic/syncthingandroid/activities/SettingsActivity.java

@@ -7,6 +7,7 @@ import android.os.AsyncTask;
 import android.os.Bundle;
 import android.preference.CheckBoxPreference;
 import android.preference.EditTextPreference;
+import android.preference.ListPreference;
 import android.preference.Preference;
 import android.preference.PreferenceFragment;
 import android.preference.PreferenceScreen;
@@ -22,6 +23,7 @@ import com.nutomic.syncthingandroid.model.Device;
 import com.nutomic.syncthingandroid.model.Options;
 import com.nutomic.syncthingandroid.service.RestApi;
 import com.nutomic.syncthingandroid.service.SyncthingService;
+import com.nutomic.syncthingandroid.util.Languages;
 import com.nutomic.syncthingandroid.views.WifiSsidPreference;
 
 import java.security.InvalidParameterException;
@@ -105,6 +107,16 @@ public class SettingsActivity extends SyncthingActivity {
             mSyncOnlyWifi.setEnabled(mAlwaysRunInBackground.isChecked());
             mSyncOnlyOnSSIDs.setEnabled(mSyncOnlyWifi.isChecked());
 
+            ListPreference languagePref = (ListPreference) findPreference(Languages.PREFERENCE_LANGUAGE);
+            Languages languages = new Languages(getActivity());
+            languagePref.setDefaultValue(Languages.USE_SYSTEM_DEFAULT);
+            languagePref.setEntries(languages.getAllNames());
+            languagePref.setEntryValues(languages.getSupportedLocales());
+            languagePref.setOnPreferenceChangeListener((p, o) -> {
+                languages.forceChangeLanguage(getActivity(), (String) o);
+                return false;
+            });
+
             mDeviceName             = (EditTextPreference) findPreference("deviceName");
             mListenAddresses        = (EditTextPreference) findPreference("listenAddresses");
             mMaxRecvKbps            = (EditTextPreference) findPreference("maxRecvKbps");

src/main/java/com/nutomic/syncthingandroid/util/Languages.java

@@ -0,0 +1,192 @@
+package com.nutomic.syncthingandroid.util;
+
+import android.annotation.SuppressLint;
+import android.annotation.TargetApi;
+import android.app.Activity;
+import android.content.Context;
+import android.content.Intent;
+import android.content.SharedPreferences;
+import android.content.res.Configuration;
+import android.content.res.Resources;
+import android.os.Build;
+import android.preference.PreferenceManager;
+import android.text.TextUtils;
+import android.util.Log;
+
+import com.nutomic.syncthingandroid.R;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.Locale;
+import java.util.Map;
+import java.util.Set;
+import java.util.TreeMap;
+
+/**
+ * Based on https://gitlab.com/fdroid/fdroidclient/blob/master/app/src/main/java/org/fdroid/fdroid/Languages.java
+ */
+public final class Languages {
+    public static final String TAG = "Languages";
+
+    public static final String USE_SYSTEM_DEFAULT = "";
+
+    private static final Locale DEFAULT_LOCALE;
+    public static final String PREFERENCE_LANGUAGE = "pref_current_language";
+
+    private final SharedPreferences mPreferences;
+    private static Map<String, String> mAvailableLanguages;
+
+    static {
+        DEFAULT_LOCALE = Locale.getDefault();
+    }
+
+    public Languages(Context context) {
+        Map<String, String> tmpMap = new TreeMap<>();
+        for (Locale locale : Arrays.asList(LOCALES_TO_TEST)) {
+            tmpMap.put(locale.getLanguage(), locale.getDisplayLanguage(locale));
+        }
+
+        // remove the current system language from the menu
+        tmpMap.remove(Locale.getDefault().getLanguage());
+
+        /* SYSTEM_DEFAULT is a fake one for displaying in a chooser menu. */
+        tmpMap.put(USE_SYSTEM_DEFAULT, context.getString(R.string.pref_language_default));
+        mAvailableLanguages = Collections.unmodifiableMap(tmpMap);
+        mPreferences = PreferenceManager.getDefaultSharedPreferences(context);
+    }
+
+    /**
+     * Handles setting the language if it is different than the current language,
+     * or different than the current system-wide locale.  The preference is cleared
+     * if the language matches the system-wide locale or "System Default" is chosen.
+     */
+    @TargetApi(17)
+    public void setLanguage(Context context) {
+        if (Build.VERSION.SDK_INT >= 24) {
+            Log.d(TAG, "Languages.setLanguage() ignored on >= android-24");
+            mPreferences.edit().remove(PREFERENCE_LANGUAGE).apply();
+            return;
+        }
+        String language = mPreferences.getString(PREFERENCE_LANGUAGE, null);
+        Locale locale;
+        if (TextUtils.equals(language, DEFAULT_LOCALE.getLanguage())) {
+            mPreferences.edit().remove(PREFERENCE_LANGUAGE).apply();
+            locale = DEFAULT_LOCALE;
+        } else if (language == null || language.equals(USE_SYSTEM_DEFAULT)) {
+            mPreferences.edit().remove(PREFERENCE_LANGUAGE).apply();
+            locale = DEFAULT_LOCALE;
+        } else {
+            /* handle locales with the country in it, i.e. zh_CN, zh_TW, etc */
+            String[] localeSplit = language.split("_");
+            if (localeSplit.length > 1) {
+                locale = new Locale(localeSplit[0], localeSplit[1]);
+            } else {
+                locale = new Locale(language);
+            }
+        }
+        Locale.setDefault(locale);
+
+        final Resources resources = context.getResources();
+        Configuration config = resources.getConfiguration();
+        if (Build.VERSION.SDK_INT >= 17) {
+            config.setLocale(locale);
+        } else {
+            config.locale = locale;
+        }
+        resources.updateConfiguration(config, resources.getDisplayMetrics());
+    }
+
+    /**
+     * Force reload the {@link Activity to make language changes take effect.}
+     *
+     * @param activity the {@code Activity} to force reload
+     */
+    @SuppressLint("ApplySharedPref")
+    public void forceChangeLanguage(Activity activity, String newLanguage) {
+        mPreferences.edit().putString(PREFERENCE_LANGUAGE, newLanguage).commit();
+        setLanguage(activity);
+        if (Build.VERSION.SDK_INT >= 24) {
+            Log.d(TAG, "Languages.forceChangeLanguage() ignored on >= android-24");
+            return;
+        }
+        Intent intent = activity.getIntent();
+        if (intent == null) { // when launched as LAUNCHER
+            return;
+        }
+        intent.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION);
+        activity.finish();
+        activity.overridePendingTransition(0, 0);
+        activity.startActivity(intent);
+        activity.overridePendingTransition(0, 0);
+    }
+
+    /**
+     * @return an array of the names of all the supported languages, sorted to
+     * match what is returned by {@link Languages#getSupportedLocales()}.
+     */
+    public String[] getAllNames() {
+        return mAvailableLanguages.values().toArray(new String[mAvailableLanguages.size()]);
+    }
+
+    /**
+     * @return sorted list of supported locales.
+     */
+    public String[] getSupportedLocales() {
+        Set<String> keys = mAvailableLanguages.keySet();
+        return keys.toArray(new String[keys.size()]);
+    }
+
+    private String capitalize(final String line) {
+        return Character.toUpperCase(line.charAt(0)) + line.substring(1);
+    }
+
+    public static final Locale[] LOCALES_TO_TEST = {
+            Locale.ENGLISH,
+            Locale.FRENCH,
+            Locale.GERMAN,
+            Locale.ITALIAN,
+            Locale.JAPANESE,
+            Locale.KOREAN,
+            Locale.SIMPLIFIED_CHINESE,
+            Locale.TRADITIONAL_CHINESE,
+            new Locale("af"),
+            new Locale("ar"),
+            new Locale("be"),
+            new Locale("bg"),
+            new Locale("ca"),
+            new Locale("cs"),
+            new Locale("da"),
+            new Locale("el"),
+            new Locale("es"),
+            new Locale("eo"),
+            new Locale("et"),
+            new Locale("eu"),
+            new Locale("fa"),
+            new Locale("fi"),
+            new Locale("he"),
+            new Locale("hi"),
+            new Locale("hu"),
+            new Locale("hy"),
+            new Locale("id"),
+            new Locale("is"),
+            new Locale("it"),
+            new Locale("ml"),
+            new Locale("my"),
+            new Locale("nb"),
+            new Locale("nl"),
+            new Locale("pl"),
+            new Locale("pt"),
+            new Locale("ro"),
+            new Locale("ru"),
+            new Locale("sc"),
+            new Locale("sk"),
+            new Locale("sn"),
+            new Locale("sr"),
+            new Locale("sv"),
+            new Locale("th"),
+            new Locale("tr"),
+            new Locale("uk"),
+            new Locale("vi"),
+    };
+
+}

src/main/res/values/strings.xml

@@ -271,6 +271,12 @@ Please report any problems you encounter via Github.</string>
         <item>None</item>
     </string-array>
 
+    <string name="preference_language_title">Language</string>
+
+    <string name="preference_language_summary">Change the app language</string>
+
+    <string name="pref_language_default">Default Language</string>
+
     <string-array name="versioning_types">
         <item>None</item>
         <item>TrashCan</item>

src/main/res/xml/app_settings.xml

@@ -49,6 +49,11 @@
             android:summary="@string/notification_type_summary"
             android:defaultValue="low_priority" />
 
+        <ListPreference
+            android:key="pref_current_language"
+            android:title="@string/preference_language_title"
+            android:summary="@string/preference_language_summary" />
+
     </PreferenceScreen>
 
     <PreferenceScreen