android: set preferred OS language on first start

frontend/drivers/platform_unix.c

@@ -2052,6 +2052,8 @@ static void frontend_unix_init(void *data)
          "setScreenOrientation", "(I)V");
    GET_METHOD_ID(env, android_app->doVibrate, class,
          "doVibrate", "(IIII)V");
+   GET_METHOD_ID(env, android_app->getUserLanguageString, class,
+         "getUserLanguageString", "()Ljava/lang/String;");
    CALL_OBJ_METHOD(env, obj, android_app->activity->clazz,
          android_app->getIntent);
 
@@ -2499,7 +2501,25 @@ enum retro_language frontend_unix_get_user_language(void)
    enum retro_language lang = RETRO_LANGUAGE_ENGLISH;
 #ifdef HAVE_LANGEXTRA
 #ifdef ANDROID
-   return RETRO_LANGUAGE_ENGLISH;
+   jstring jstr = NULL;
+   JNIEnv *env = jni_thread_getenv();
+
+   if (!env || !g_android)
+      return lang;
+
+   if (g_android->getUserLanguageString)
+   {
+      CALL_OBJ_METHOD(env, jstr, g_android->activity->clazz, g_android->getUserLanguageString);
+
+      if (jstr)
+      {
+         const char *langStr = (*env)->GetStringUTFChars(env, jstr, 0);
+
+         lang = rarch_get_language_from_iso(langStr);
+
+         (*env)->ReleaseStringUTFChars(env, jstr, langStr);
+      }
+   }
 #else
    lang = rarch_get_language_from_iso(getenv("LANG"));
 #endif

frontend/drivers/platform_unix.h

@@ -163,6 +163,7 @@ struct android_app
    jmethodID getBatteryLevel;
    jmethodID setSustainedPerformanceMode;
    jmethodID setScreenOrientation;
+   jmethodID getUserLanguageString;
    jmethodID doVibrate;
 };
 

pkg/android/phoenix/src/com/retroarch/browser/retroactivity/RetroActivityCommon.java

@@ -21,6 +21,7 @@ import android.os.VibrationEffect;
 import android.util.Log;
 import java.lang.Math;
 import java.util.concurrent.CountDownLatch;
+import java.util.Locale;
 
 /**
  * Class which provides common methods for RetroActivity related classes.
@@ -153,6 +154,20 @@ public class RetroActivityCommon extends RetroActivityLocation
     });
   }
 
+  public String getUserLanguageString()
+  {
+    String lang = Locale.getDefault().getLanguage();
+    String country = Locale.getDefault().getCountry();
+
+    if (lang.length() == 0)
+      return "en";
+
+    if (country.length() == 0)
+      return lang;
+
+    return lang + '_' + country;
+  }
+
   @TargetApi(24)
   public void setSustainedPerformanceMode(boolean on)
   {