<!--permission for internet-->
<uses-permission android:name="android.permission.INTERNET"/>

<?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">

    <!--edit text to enter your input-->
    <EditText
        android:id="@+id/idEdtLanguage"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="50dp"
        android:hint="Enter your name to translate"
        android:padding="4dp"
        android:textColor="@color/black"
        android:textSize="20sp" />

    <!--button to translate language of the input text-->
    <Button
        android:id="@+id/idBtnTranslateLanguage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/idTVTranslatedLanguage"
        android:layout_centerInParent="true"
        android:text="Translate language" />

    <!--text view to display the translated text-->
    <TextView
        android:id="@+id/idTVTranslatedLanguage"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/idEdtLanguage"
        android:layout_centerHorizontal="true"
        android:layout_margin="20dp"
        android:gravity="center_horizontal"
        android:text="Translated language"
        android:textAlignment="center"
        android:textSize="20sp" />

</RelativeLayout>

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.OnSuccessListener;
import com.google.firebase.ml.common.modeldownload.FirebaseModelDownloadConditions;
import com.google.firebase.ml.naturallanguage.FirebaseNaturalLanguage;
import com.google.firebase.ml.naturallanguage.translate.FirebaseTranslateLanguage;
import com.google.firebase.ml.naturallanguage.translate.FirebaseTranslator;
import com.google.firebase.ml.naturallanguage.translate.FirebaseTranslatorOptions;

public class MainActivity extends AppCompatActivity {

    // creating variables for our image view, 
    // text view and two buttons.
    private EditText edtLanguage;
    private TextView translateLanguageTV;
    private Button translateLanguageBtn;

    // create a variable for our 
    // firebase language translator.
    FirebaseTranslator englishGermanTranslator;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // on below line we are creating our firebase translate option.
        FirebaseTranslatorOptions options =
                new FirebaseTranslatorOptions.Builder()
                        // below line we are specifying our source language.
                        .setSourceLanguage(FirebaseTranslateLanguage.EN)
                        // in below line we are displaying our target language.
                        .setTargetLanguage(FirebaseTranslateLanguage.DE)
                        // after that we are building our options.
                        .build();
        // below line is to get instance
        // for firebase natural language.
        englishGermanTranslator = FirebaseNaturalLanguage.getInstance().getTranslator(options);

        // on below line we are initializing our variables.
        edtLanguage = findViewById(R.id.idEdtLanguage);
        translateLanguageTV = findViewById(R.id.idTVTranslatedLanguage);
        translateLanguageBtn = findViewById(R.id.idBtnTranslateLanguage);

        // adding on click listener for button
        translateLanguageBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // calling method to download language 
                // modal to which we have to translate.
                String string = edtLanguage.getText().toString();
                downloadModal(string);
            }
        });
    }

    private void downloadModal(String input) {
        // below line is use to download the modal which
        // we will require to translate in german language
        FirebaseModelDownloadConditions conditions = new FirebaseModelDownloadConditions.Builder().requireWifi().build();

        // below line is use to download our modal.
        englishGermanTranslator.downloadModelIfNeeded(conditions).addOnSuccessListener(new OnSuccessListener<Void>() {
            @Override
            public void onSuccess(Void aVoid) {

                // this method is called when modal is downloaded successfully.
                Toast.makeText(MainActivity.this, "Please wait language modal is being downloaded.", Toast.LENGTH_SHORT).show();

                // calling method to translate our entered text.
                translateLanguage(input);

            }
        }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Toast.makeText(MainActivity.this, "Fail to download modal", Toast.LENGTH_SHORT).show();
            }
        });
    }

    private void translateLanguage(String input) {
        englishGermanTranslator.translate(input).addOnSuccessListener(new OnSuccessListener<String>() {
            @Override
            public void onSuccess(String s) {
                translateLanguageTV.setText(s);
            }
        }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Toast.makeText(MainActivity.this, "Fail to translate", Toast.LENGTH_SHORT).show();
            }
        });
    }
}