How to change app language when user selects language in Android ?

• Add the following code to res/layout/activity_main.xml.

<RelativeLayout
   xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:id="@+id/rl"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   android:padding="10dp"
   tools:context=".MainActivity">
   <Spinner
      android:id="@+id/spinner"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_centerInParent="true" />
   <TextView
      android:id="@+id/string"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="@string/thank_you"
      android:textSize="24sp"
      android:layout_centerInParent="true"
      android:layout_below="@id/spinner"/>
</RelativeLayout>

•    Add the following code to src/MainActivity.java

import android.content.Intent;
import android.content.res.Configuration;
import android.content.res.Resources;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
public class MainActivity extends AppCompatActivity {
   Spinner spinner;
   Locale locale;
   String currentLanguage = "en", currentLang;
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      currentLanguage = getIntent().getStringExtra(currentLang);
      spinner = findViewById(R.id.spinner);
      List<String> list = new ArrayList<>();
      list.add("Select Language");
      list.add("English");
      list.add("Español");
      list.add("Français");
      list.add("Hindi");
      ArrayAdapter<String> adapter = new ArrayAdapter<>(this, R.layout.support_simple_spinner_dropdown_item, list);
      adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
      spinner.setAdapter(adapter);
      spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
         @Override
         public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            switch (position) {
               case 0:
               break;
               case 1:
                  setLocale("en");
               break;
               case 2:
                  setLocale("es");
               break;
               case 3:
                  setLocale("fr");
               break;
               case 4:
                  setLocale("hi");
               break;
            }
         }
         @Override
         public void onNothingSelected(AdapterView<?> parent) {
         }
      });
   }
   private void setLocale(String localeName) {
      if (!localeName.equals(currentLanguage)) {
         locale = new Locale(localeName);
         Resources res = getResources();
         DisplayMetrics dm = res.getDisplayMetrics();
         Configuration conf = res.getConfiguration();
         conf.locale = locale;
         res.updateConfiguration(conf, dm);
         Intent refresh = new Intent(this,
         MainActivity.class);
         refresh.putExtra(currentLang, localeName);
         startActivity(refresh);
      } else {
         Toast.makeText(MainActivity.this, "Language
         already selected!", Toast.LENGTH_SHORT).show();
      }
   }
   public void onBackPressed() {
      Intent intent = new Intent(Intent.ACTION_MAIN);
      intent.addCategory(Intent.CATEGORY_HOME);
      intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
      startActivity(intent);
      finish();
      System.exit(0);
   }
}

•    values-hi/strings.xml

<resources>
   <string name="app_name">Sample</string>
   <string name="thank_you">धन्यवाद</string>
</resources>

•    values-fr/strings.xml

<resources>
   <string name="app_name">Sample</string>
   <string name="thank_you">Je vous remercie</string>
</resources>

•    values-es/strings.xml

<resources>
   <string name="app_name">Sample</string>
   <string name="thank_you">Gracias</string>
</resources>

strings.xml

<resources>
   <string name="app_name">Sample</string>
   <string name="thank_you">Thank you</string>
</resources>

Step 5 − Add the following code to androidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest
   xmlns:android="http://schemas.android.com/apk/res/android"
   package="app.com.sample">
   <application
      android:allowBackup="true"
      android:icon="@mipmap/ic_launcher"
      android:label="@string/app_name"
      android:roundIcon="@mipmap/ic_launcher_round"
      android:supportsRtl="true"
      android:theme="@style/AppTheme">
      <activity android:name=".MainActivity">
         <intent-filter>
            <action
               android:name="android.intent.action.MAIN" />
            <category
               android:name="android.intent.category.LAUNCHER" />
         </intent-filter>
      </activity>
   </application>
</manifest>

OutPut