Android how to change the application language at runtime and make it persistent using preference manager

gistfile1.txt

package com.nkdroid.firstaid.translate_app;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;

import android.view.View;
import android.view.WindowManager;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;
import java.util.Locale;

import android.content.res.Configuration;
import android.content.res.Resources;
import android.util.DisplayMetrics;

import android.widget.AdapterView;
import android.widget.Spinner;
import android.content.SharedPreferences;

import android.preference.PreferenceManager;
import android.widget.AdapterView.OnItemSelectedListener;

import com.nkdroid.firstaid.R;



public class HelloActivity extends AppCompatActivity {

    private Spinner countrySpinner;
    private Spinner genderSpinner;
    private String key= "Help Yourself";
    private boolean isitShowed;

    private View firstView;

    private Button startButton;
    private TextView ageTextView;
    private TextView termsTextView;
    Locale myLocale;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
        SharedPreferences.Editor editor = preferences.edit();

        boolean ciao_1=preferences.getBoolean(key,isitShowed);
        //Log.d("intro",ciao+"");
        if(ciao_1){
            loadMainActivity();
        }

        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_localize);

        // Prevent SoftKeyboard to pop up on start
        getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_HIDDEN);

        countrySpinner = (Spinner) findViewById(R.id.activity_hello_spinner_country);
        //  genderSpinner = (Spinner) findViewById(R.id.activity_hello_spinner_gender);
        startButton = (Button) findViewById(R.id.activity_hello_button_start);
        termsTextView = (TextView) findViewById(R.id.helloactivity_textview_terms);
        // ageTextView = (TextView) findViewById(R.id.activity_hello_age);


        countrySpinner.setOnItemSelectedListener(new OnItemSelectedListener() {

            public void onItemSelected(AdapterView<?> parent, View view,
                                       int pos, long id) {

                if (pos == 1) {

                    Toast.makeText(parent.getContext(),
                            "You have selected English", Toast.LENGTH_SHORT)
                            .show();
                    setLocale("en");
                } else if (pos == 2) {

                    Toast.makeText(parent.getContext(),
                            "Vous avez choisi le français", Toast.LENGTH_SHORT)
                            .show();
                    setLocale("fr");
                }

            }

            public void onNothingSelected(AdapterView<?> arg0) {
                // TODO Auto-generated method stub
            }

        });

    }
    public void setLocale(String lang) {

        myLocale = new Locale(lang);
        Resources res = getResources();
        DisplayMetrics dm = res.getDisplayMetrics();
        Configuration conf = res.getConfiguration();
        conf.locale = myLocale;
        res.updateConfiguration(conf, dm);


        startActivity(new Intent(HelloActivity.this, com.nkdroid.firstaid.doctorfinder.activity.access.SplashActivity.class));
        finish();
    }

    private void loadMainActivity() {;

        SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(this);
        SharedPreferences.Editor editor = preferences.edit();
        isitShowed=true;
        editor.putBoolean(key, isitShowed);
        editor.apply();

        Intent intent = new Intent(this,com.nkdroid.firstaid.doctorfinder.activity.access.SplashActivity.class);
        // Intent intent = new Intent(this,com.nkdroid.firstaid.HomeActivity.class);
        startActivity(intent);
        finish();
    }


}

gistfile2.txt

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:custom="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/helloactivity_mainframe"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:visibility="visible"
    tools:context="com.nkdroid.firstaid.translate_app.HelloActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:paddingBottom="32dp"
        android:paddingLeft="32dp"
        android:paddingRight="32dp"
        android:paddingTop="32dp">

        <TextView
            android:id="@+id/activity_hello_title"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:paddingTop="32dp"
            android:text="@string/helloactivity_headline"
            android:textColor="#000000"
            android:textSize="@dimen/abc_text_size_display_1_material" />

        <TextView
            android:id="@+id/activity_hello_subtitle"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:paddingTop="16dp"
            android:text="@string/helloactivity_subhead"
            android:textColor="#323232"
            android:textSize="@dimen/abc_text_size_subhead_material" />

        <Spinner
            android:id="@+id/activity_hello_spinner_country"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="20dp"
            android:entries="@array/languages"
             />





        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="16dp"
            android:text="@string/helloactivity_hint_settings"
            android:textStyle="bold" />

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="32dp"
            android:text="@string/helloactivity_textview_tos"
            android:textColor="#323232"
            android:textStyle="bold" />

        <TextView
            android:id="@+id/helloactivity_textview_terms"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="8dp"
            android:text="@string/helloactivity_terms"
            android:textColor="#07A7CE"
            android:textStyle="bold" />

        <android.support.v7.widget.AppCompatButton
            android:id="@+id/activity_hello_button_start"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="right"
            android:layout_marginTop="24dp"
            android:background="?android:attr/selectableItemBackground"
            android:drawableEnd="@drawable/ic_navigate_next_pink_24px"
            android:drawableRight="@drawable/ic_navigate_next_pink_24px"
            android:padding="8dp"
            android:text="@string/helloactivity_button_start"
            android:textColor="#07A7CE"
            android:textStyle="bold" />
    </LinearLayout>
</ScrollView>