How to change the app language programmatically in android?

This example demonstrates how do I in change the app language programmatically android.
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.
Step 2 − Add the following code to res/layout/activity_main.xml.
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
   xmlns:android="http://schemas.android.com/apk/res/android"
   xmlns:tools="http://schemas.android.com/tools"
   android:layout_width="match_parent"
   android:layout_height="match_parent"
   tools:context=".MainActivity">
   <TextView
      android:id="@+id/textView"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:text="@string/hello_world"
      android:textSize="30dp"
      android:textStyle="bold"
      android:textColor="@color/colorPrimary"
      android:layout_centerInParent="true"/>
</RelativeLayout>
Step 3 − Add the following code to src/MainActivity.java
import android.content.res.Configuration;
import android.content.res.Resources;
import android.os.Build;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.DisplayMetrics;
import java.util.Locale;
public class MainActivity extends AppCompatActivity {
   @Override
   protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setAppLocale("bg");
      setContentView(R.layout.activity_main);
   }
   private void setAppLocale(String localeCode){
      Resources resources = getResources();
      DisplayMetrics dm = resources.getDisplayMetrics();
      Configuration config = resources.getConfiguration();
      if (Build.VERSION.SDK_INT>=Build.VERSION_CODES.JELLY_BEAN_MR1){
         config.setLocale(new Locale(localeCode.toLowerCase()));
      } else {
         config.locale = new Locale(localeCode.toLowerCase());
      }
      resources.updateConfiguration(config, dm);
   }
}
Step 4 − Right click on res → Click New → File. Name the file as value-bg/strings.xml and add following code
<resources>
   <string name="app_name">Sample</string>
   <string name="hello_world">дравей свят</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>
Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click Run  icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen −
Click here to download the project code.