get preferred locales on android

android-project/app/proguard-rules.pro

@@ -50,6 +50,8 @@
     boolean supportsRelativeMouse();
     int openFileDescriptor(java.lang.String, java.lang.String);
     boolean showFileDialog(java.lang.String[], boolean, boolean, int);
+    java.lang.String getPreferredLocales();
+    java.lang.String formatLocale(java.util.Locale);
 }
 
 -keep,includedescriptorclasses,allowoptimization class org.libsdl.app.HIDDeviceManager {

android-project/app/src/main/java/org/libsdl/app/SDLActivity.java

@@ -23,6 +23,7 @@ import android.net.Uri;
 import android.os.Build;
 import android.os.Bundle;
 import android.os.Handler;
+import android.os.LocaleList;
 import android.os.Message;
 import android.os.ParcelFileDescriptor;
 import android.util.DisplayMetrics;
@@ -2116,6 +2117,48 @@ public class SDLActivity extends Activity implements View.OnSystemUiVisibilityCh
         int requestCode;
         boolean multipleChoice;
     }
+    
+    /**
+     * This method is called by SDL using JNI.
+     */
+    public static String getPreferredLocales() {
+        String result = "";
+        if (Build.VERSION.SDK_INT >= 24 /* Android 7 (N) */) {
+            LocaleList locales = LocaleList.getAdjustedDefault();
+            for (int i = 0; i < locales.size(); i++) {
+                if (i != 0) result += ",";
+                result += formatLocale(locales.get(i));
+            }
+        }
+        else if (mCurrentLocale != null) {
+            result = formatLocale(mCurrentLocale);
+        }
+        return result;
+    }
+
+    public static String formatLocale(Locale locale) {
+        String result = "";
+        String lang = "";
+        if (locale.getLanguage() == "in") {
+            // Indonesian is "id" according to ISO 639.2, but on Android is "in" because of Java backwards compatibility
+            lang = "id";
+        }
+        else if (locale.getLanguage() == "") {
+            // Make sure language is never empty
+            lang = "und";
+        }
+        else {
+            lang = locale.getLanguage();
+        }
+
+        if (locale.getCountry() == "") {
+            result = lang;
+        }
+        else {
+            result = lang + "_" + locale.getCountry();
+        }
+        return result;
+    }
 }
 
 /**