Enable localization for app strings

A setting has been added to override the system default language, should a user want a different language for the app.

app/build.gradle

@@ -40,6 +40,13 @@ android {
 
         // Only enable separate process for release builds
         manifestPlaceholders += [emulationProcess: ""]
+
+        def locales = ["en", "de", "el", "es", "es-419", "fr", "hu", "id", "it", "ja", "ko", "pl", "ru", "ta", "zh-Hans", "zh-Hant"]
+
+        // Add available locales to the build config so that they can be accessed from the app
+        buildConfigField "String[]", "AVAILABLE_APP_LANGUAGES", "new String[]{\"" + locales.join("\",\"") + "\"}"
+        // Uncomment the following line whenever AAPT2 will properly support BCP47 language tags
+        //resourceConfigurations += locales
     }
 
     /* JVM Bytecode Options */

app/src/main/AndroidManifest.xml

@@ -20,6 +20,7 @@
         android:icon="@drawable/logo_skyline"
         android:isGame="true"
         android:label="${appLabel}"
+        android:localeConfig="@xml/locales_config"
         android:supportsRtl="true"
         android:theme="@style/AppTheme"
         tools:ignore="GoogleAppIndexingWarning,UnusedAttribute">
@@ -116,6 +117,15 @@
             </intent-filter>
         </provider>
 
+        <service
+            android:name="androidx.appcompat.app.AppLocalesMetadataHolderService"
+            android:enabled="false"
+            android:exported="false">
+            <meta-data
+                android:name="autoStoreLocales"
+                android:value="true" />
+        </service>
+
         <meta-data
             android:name="com.android.graphics.injectLayers.enable"
             android:value="true" />

app/src/main/java/emu/skyline/preference/LanguagePreference.kt

@@ -0,0 +1,44 @@
+/*
+ * SPDX-License-Identifier: MPL-2.0
+ * Copyright © 2023 Skyline Team and Contributors (https://github.com/skyline-emu/)
+ */
+
+package emu.skyline.preference
+
+import android.content.Context
+import android.util.AttributeSet
+import androidx.appcompat.app.AppCompatDelegate
+import androidx.core.os.LocaleListCompat
+import androidx.preference.ListPreference
+import androidx.preference.Preference.OnPreferenceChangeListener
+import androidx.preference.Preference.SummaryProvider
+import emu.skyline.BuildConfig
+import emu.skyline.R
+import java.util.*
+
+private const val SystemLanguage = "syslang"
+
+class LanguagePreference @JvmOverloads constructor(context : Context, attrs : AttributeSet? = null, defStyleAttr : Int = androidx.preference.R.attr.preferenceStyle) : ListPreference(context, attrs, defStyleAttr) {
+    init {
+        entries = arrayOf(systemEntry) + BuildConfig.AVAILABLE_APP_LANGUAGES.map { Locale.forLanguageTag(it).run { getDisplayName(this) } }
+        entryValues = arrayOf(SystemLanguage) + BuildConfig.AVAILABLE_APP_LANGUAGES
+
+        value = AppCompatDelegate.getApplicationLocales()[0]?.toLanguageTag() ?: SystemLanguage
+
+        onPreferenceChangeListener = OnPreferenceChangeListener { _, newValue ->
+            if (newValue == SystemLanguage) {
+                AppCompatDelegate.setApplicationLocales(LocaleListCompat.getEmptyLocaleList())
+            } else {
+                val newLocale = LocaleListCompat.forLanguageTags(newValue as String)
+                AppCompatDelegate.setApplicationLocales(newLocale)
+            }
+            true
+        }
+
+        summaryProvider = SummaryProvider<ListPreference> {
+            AppCompatDelegate.getApplicationLocales()[0]?.displayName ?: systemEntry
+        }
+    }
+
+    private val systemEntry : String get() = context.getString(R.string.app_language_default)
+}

app/src/main/res/values/strings.xml

@@ -41,6 +41,8 @@
     <!-- Settings - Appearance -->
     <string name="appearance">Appearance</string>
     <string name="theme">Theme</string>
+    <string name="app_language">App Language</string>
+    <string name="app_language_default">Use System Default</string>
     <string name="layout_type">Game Display Layout</string>
     <string name="sort_apps_by">Games Sorting Order</string>
     <string name="group_by_format">Group Games By Format</string>

app/src/main/res/xml/app_preferences.xml

@@ -28,6 +28,10 @@
             app:key="app_theme"
             app:title="@string/theme"
             app:useSimpleSummaryProvider="true" />
+        <emu.skyline.preference.LanguagePreference
+            app:key="app_language"
+            app:persistent="false"
+            app:title="@string/app_language" />
         <emu.skyline.preference.IntegerListPreference
             android:defaultValue="1"
             android:entries="@array/layout_type"

app/src/main/res/xml/locales_config.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="utf-8"?>
+<locale-config xmlns:android="http://schemas.android.com/apk/res/android">
+    <locale android:name="en" /> <!-- English (default) -->
+    <locale android:name="de" /> <!-- German -->
+    <locale android:name="el" /> <!-- Greek -->
+    <locale android:name="es" /> <!-- Spanish -->
+    <locale android:name="es-419" /> <!-- Latin American Spanish -->
+    <locale android:name="fr" /> <!-- French -->
+    <locale android:name="hu" /> <!-- Hungarian -->
+    <locale android:name="id" /> <!-- Indonesian -->
+    <locale android:name="it" /> <!-- Italian -->
+    <locale android:name="ja" /> <!-- Japanese -->
+    <locale android:name="ko" /> <!-- Korean -->
+    <locale android:name="pl" /> <!-- Polish -->
+    <locale android:name="ru" /> <!-- Russian -->
+    <locale android:name="ta" /> <!-- Tamil -->
+    <locale android:name="zh-Hans" /> <!-- Simplified Chinese -->
+    <locale android:name="zh-Hant" /> <!-- Traditional Chinese -->
+</locale-config>