Force locale for Android flavor with resConfig

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Well, after many hours, here’s the solution to my problem for those ending up with the same problem.

Turns out that resConfig is not for what I though. The proper and only way I found to force the locale for a specific flavor is like this:

First, make sure all your activities extends a common activity which will be responsible to force the locale. (I had to create 2 since I have some activities extending FragmentActivity and some extending Activity. I also don’t really like doing so in the Activities constructor but since I have to call applyOverrideConfiguration before any call is done on getResources, I need to call it before the activity’s onStart).

public class LocaleMainActivity extends Activity {

    public LocaleMainActivity() {
        ActivityUtils.forceLocale(this);
    }
}

public class LocaleMainFragmentActivity extends FragmentActivity {

    public LocaleMainFragmentActivity() {
        ActivityUtils.forceLocale(this);
    }
}

//Method from ActivityUtils
public static void forceLocale(ContextThemeWrapper contextThemeWrapper) {
    Configuration configuration = new Configuration();
    Locale defaultLocale = new Locale(BuildConfig.LOCALE);
    configuration.locale = defaultLocale;
    contextThemeWrapper.applyOverrideConfiguration(configuration);      
}

Next, you need to define the locale in your build.gradle flavors

productFlavors {

    myFrenchFlavor {
     buildConfigField "String", "LOCALE", "\"fr\""
    }
    myEnglishFlavor {
      buildConfigField "String", "LOCALE", "\"en\""
    }
}

I tested the solution on API 19+. Works when you change language while in the app too.

Alternate solution (won’t work on Android M+ see android bug report)
This solution is wide spreaded on stackOverflow but I faced a wall while implementing this on Android M so keep this in mind.

In the onCreate() of your AndroidApplication you can call updateConfiguration with the locale set.

Locale myLocale = new Locale(BuildConfig.LOCALE);
Resources res = getResources();
Configuration conf = res.getConfiguration();
conf.locale = myLocale;
res.updateConfiguration(conf, res.getDisplayMetrics());

You will also need to reset it if you defined onConfigurationChanged()

@Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);            
        Configuration config = new Configuration(newConfig);
        config.locale = new Locale(BuildConfig.LOCALE);
        getBaseContext().getResources().updateConfiguration(config, getBaseContext().getResources().getDisplayMetrics());
    }

EDIT: Be aware that this applyOverrideConfiguration currently has a side effect which is explained here Chromium webview does not seems to work with Android applyOverrideConfiguration. The Chromium team are currently working on it!

Thanks.

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