While developing your awesome application, sometimes you are required to add a language change feature to your app on the fly. However, Android OS does not directly support this behaviour. And therefore, you need to solve this situation in some other ways. For more details see http://gunhansancar.com/change-language-programmatically-in-android/

LocaleHelper.java

package com.gunhansancar.changelanguageexample.helper;

import android.annotation.TargetApi;
import android.content.Context;
import android.content.SharedPreferences;
import android.content.res.Configuration;
import android.content.res.Resources;
import android.os.Build;
import android.preference.PreferenceManager;

import java.util.Locale;

/**
 * This class is used to change your application locale and persist this change for the next time
 * that your app is going to be used.
 * <p/>
 * You can also change the locale of your application on the fly by using the setLocale method.
 * <p/>
 * Created by gunhansancar on 07/10/15.
 */
public class LocaleHelper {

	private static final String SELECTED_LANGUAGE = "Locale.Helper.Selected.Language";

	public static Context onAttach(Context context) {
		String lang = getPersistedData(context, Locale.getDefault().getLanguage());
		return setLocale(context, lang);
	}

	public static Context onAttach(Context context, String defaultLanguage) {
		String lang = getPersistedData(context, defaultLanguage);
		return setLocale(context, lang);
	}

	public static String getLanguage(Context context) {
		return getPersistedData(context, Locale.getDefault().getLanguage());
	}

	public static Context setLocale(Context context, String language) {
		persist(context, language);

		if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
			return updateResources(context, language);
		}

		return updateResourcesLegacy(context, language);
	}

	private static String getPersistedData(Context context, String defaultLanguage) {
		SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(context);
		return preferences.getString(SELECTED_LANGUAGE, defaultLanguage);
	}

	private static void persist(Context context, String language) {
		SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(context);
		SharedPreferences.Editor editor = preferences.edit();

		editor.putString(SELECTED_LANGUAGE, language);
		editor.apply();
	}

	@TargetApi(Build.VERSION_CODES.N)
	private static Context updateResources(Context context, String language) {
		Locale locale = new Locale(language);
		Locale.setDefault(locale);

		Configuration configuration = context.getResources().getConfiguration();
		configuration.setLocale(locale);
		configuration.setLayoutDirection(locale);

		return context.createConfigurationContext(configuration);
	}

	@SuppressWarnings("deprecation")
	private static Context updateResourcesLegacy(Context context, String language) {
		Locale locale = new Locale(language);
		Locale.setDefault(locale);

		Resources resources = context.getResources();

		Configuration configuration = resources.getConfiguration();
		configuration.locale = locale;
		if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
			configuration.setLayoutDirection(locale);
		}

		resources.updateConfiguration(configuration, resources.getDisplayMetrics());

		return context;
	}
}