Сделаны все пункты из задач

android/app/src/main/java/com/dinect/checker/MainActivity.java

@@ -15,6 +15,8 @@ import com.dinect.checker.zbar.CameraActivity;
 import com.dinect.checker.zxing.ScannerActivity;
 
 import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
 import java.util.Locale;
 import java.util.Map;
 
@@ -66,7 +68,7 @@ public class MainActivity extends FlutterActivity {
     private void callMethod(MethodCall call, Result result) {
         switch (call.method) {
             case "getLocale":
-                result.success(Locale.getDefault().getLanguage());
+                result.success(getLanguage());
                 break;
             case "getFlavor":
                 result.success(BuildConfig.flavor);
@@ -93,6 +95,15 @@ public class MainActivity extends FlutterActivity {
         }
     }
 
+    private String getLanguage() {
+        List<String> availableLanguages = Arrays.asList("ru", "en");
+        if (availableLanguages.contains(Locale.getDefault().getLanguage())) {
+            return Locale.getDefault().getLanguage();
+        } else {
+            return BuildConfig.locale;
+        }
+    }
+
     private void checkInternetConnection(Result result) {
         boolean connected = Utils.isOnline(this);
         if (!connected)