Change the language / locale of my app with Oreo 8.0 phones doesn't work properly

Question

I can perfectly change the language into my app and it works with every activity. Never had any problems (with my S4, and my friend's phones). But when I do it with my S9 (Oreo 8.0) nothing works. The language changes for some things but the most part of my app doesn't change the language. I don't understand, what changed with oreo that doesn't work anymore with what I did?

Here is what I do to change it (the example is for spanish language):

   private View.OnClickListener btnLangue3Listener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            langue.setBackground(ResourcesCompat.getDrawable(getResources(), R.mipmap.spanishflag, null));
  langueMenu.setVisibility(View.GONE);
            if (Locale.getDefault().getLanguage().equals("fr") || Locale.getDefault().getLanguage().equals("en")) {
                Context context = getApplicationContext();
                changeLang(context ,"es");
                saveLocale("es");
                restartActivity();
  }


        }
    };



private void restartActivity() {
        Intent mStartActivity = new Intent(getApplicationContext(), SplashActivity.class);

        finish();
        CharSequence text = getApplicationContext().getResources().getString(R.string.messageLang);
        int duration = Toast.LENGTH_LONG;

        Toast toast = Toast.makeText(this, text, duration);
        toast.show();


        int secs = 14; // Delay in seconds

        Utils.delay(secs, new Utils.DelayCallback() {
            @Override
            public void afterDelay() {
                Intent mStartActivity = new Intent(getApplicationContext(), SplashActivity.class);
                int mPendingIntentId = 123456;
                PendingIntent mPendingIntent = PendingIntent.getActivity(getApplicationContext(), mPendingIntentId, mStartActivity, PendingIntent.FLAG_CANCEL_CURRENT);
                AlarmManager mgr = (AlarmManager) getApplicationContext().getSystemService(Context.ALARM_SERVICE);
                mgr.set(AlarmManager.RTC, System.currentTimeMillis() + 100, mPendingIntent);
                System.exit(0);
            }


        });
    }


 public void loadLocale() {
        String langPref = "Language";
        SharedPreferences prefs = getSharedPreferences("CommonPrefs",
                Activity.MODE_PRIVATE);
        String language = prefs.getString(langPref, "");
        changeLang(getApplicationContext(), language);
    }

    public void changeLang(Context context, String lang) {
        if (lang.equalsIgnoreCase(""))
            return;
        Locale locale = new Locale(lang);
        Locale.setDefault(locale);
        Configuration config = getApplicationContext().getResources().getConfiguration();
        config.setLocale(locale);
        getApplicationContext().createConfigurationContext(config);
        getApplicationContext().getResources().updateConfiguration(config, getApplicationContext().getResources().getDisplayMetrics());
}

    public void saveLocale(String lang) {
        String langPref = "Language";
        SharedPreferences prefs = getSharedPreferences("CommonPrefs",
                Activity.MODE_PRIVATE);
        SharedPreferences.Editor editor = prefs.edit();
        editor.putString(langPref, lang);
        editor.commit();
    }

tl;dr: I change the locale to "es", restart the activity and the app (wasn't working if I wasn't restarting the app) and save it in a sharedpreferences. Once an activity opens I retrieve the shared preferences and use it as a locale like this: First I call loadLocale(); then :

  public void loadLocale() {
        String langPref = "Language";
        SharedPreferences prefs = getSharedPreferences("CommonPrefs",
                Activity.MODE_PRIVATE);
        String language = prefs.getString(langPref, "");
        changeLang(language);
    }
    public void changeLang(String lang) {


        if (lang.equalsIgnoreCase(""))
            return;
        Locale myLocale = new Locale(lang);
        saveLocale(lang);
        Locale.setDefault(myLocale);


        Configuration config = getApplicationContext().getResources().getConfiguration();
        config.setLocale(myLocale);
        this.createConfigurationContext(config);
        this.getResources().updateConfiguration(config, getApplicationContext().getResources().getDisplayMetrics());
    }

    public void saveLocale(String lang) {
        String langPref = "Language";
        SharedPreferences prefs = getSharedPreferences("CommonPrefs",
                Activity.MODE_PRIVATE);
        SharedPreferences.Editor editor = prefs.edit();
        editor.putString(langPref, lang);
        editor.commit();
    }

What do I do wrong? Is there a simplier or better way to do it? I searched everywhere and nothing worked...