Add in-app language selector

app/src/main/res/resources.properties

@@ -0,0 +1 @@
+unqualifiedResLocale=en

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

@@ -3,6 +3,8 @@
     <!-- App -->
     <string name="app_name" translatable="false">sing-box</string>
     <string name="app_version_title">نسخه برنامه</string>
+    <string name="language">زبان</string>
+    <string name="system_default">پیش‌فرض سیستم</string>
 
     <!-- Common Actions -->
     <string name="ok">تأیید</string>

app/src/main/res/values-ru-rRU/strings.xml

@@ -3,6 +3,8 @@
     <!-- App -->
     <string name="app_name" translatable="false">sing-box</string>
     <string name="app_version_title">Версия приложения</string>
+    <string name="language">Язык</string>
+    <string name="system_default">Системный по умолчанию</string>
 
     <!-- Common Actions -->
     <string name="ok">OK</string>

app/src/main/res/values-zh-rCN/strings.xml

@@ -3,6 +3,8 @@
     <!-- App -->
     <string name="app_name" translatable="false">sing-box</string>
     <string name="app_version_title">应用版本</string>
+    <string name="language">语言</string>
+    <string name="system_default">跟随系统</string>
 
     <!-- Common Actions -->
     <string name="ok">好</string>

app/src/main/res/values-zh-rTW/strings.xml

@@ -3,6 +3,8 @@
     <!-- App -->
     <string name="app_name" translatable="false">sing-box</string>
     <string name="app_version_title">應用程式版本</string>
+    <string name="language">語言</string>
+    <string name="system_default">跟隨系統</string>
 
     <!-- Common Actions -->
     <string name="ok">確定</string>

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

@@ -3,6 +3,8 @@
     <!-- App -->
     <string name="app_name" translatable="false">sing-box</string>
     <string name="app_version_title">App version</string>
+    <string name="language">Language</string>
+    <string name="system_default">System default</string>
 
     <!-- Common Actions -->
     <string name="ok">OK</string>