activity_main.xmlMainActivity.java
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:padding="16dp"
    tools:context="com.codinginflow.texttospeechexample.MainActivity">

    <EditText
        android:id="@+id/edit_text"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        android:hint="Enter Text" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Pitch"
        android:textSize="16sp" />

    <SeekBar
        android:id="@+id/seek_bar_pitch"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:progress="50" />

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Speed"
        android:textSize="16sp" />

    <SeekBar
        android:id="@+id/seek_bar_speed"
        android:layout_width="200dp"
        android:layout_height="wrap_content"
        android:layout_marginBottom="16dp"
        android:progress="50" />

    <Button
        android:id="@+id/button_speak"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:enabled="false"
        android:text="Say it!" />

</LinearLayout>

package com.codinginflow.texttospeechexample;

import android.speech.tts.TextToSpeech;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.SeekBar;

import java.util.Locale;

public class MainActivity extends AppCompatActivity {
    private TextToSpeech mTTS;
    private EditText mEditText;
    private SeekBar mSeekBarPitch;
    private SeekBar mSeekBarSpeed;
    private Button mButtonSpeak;

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

        mButtonSpeak = findViewById(R.id.button_speak);

        mTTS = new TextToSpeech(this, new TextToSpeech.OnInitListener() {
            @Override
            public void onInit(int status) {
                if (status == TextToSpeech.SUCCESS) {
                    int result = mTTS.setLanguage(Locale.GERMAN);

                    if (result == TextToSpeech.LANG_MISSING_DATA
                            || result == TextToSpeech.LANG_NOT_SUPPORTED) {
                        Log.e("TTS", "Language not supported");
                    } else {
                        mButtonSpeak.setEnabled(true);
                    }
                } else {
                    Log.e("TTS", "Initialization failed");
                }
            }
        });

        mEditText = findViewById(R.id.edit_text);
        mSeekBarPitch = findViewById(R.id.seek_bar_pitch);
        mSeekBarSpeed = findViewById(R.id.seek_bar_speed);

        mButtonSpeak.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                speak();
            }
        });
    }

    private void speak() {
        String text = mEditText.getText().toString();
        float pitch = (float) mSeekBarPitch.getProgress() / 50;
        if (pitch < 0.1) pitch = 0.1f;
        float speed = (float) mSeekBarSpeed.getProgress() / 50;
        if (speed < 0.1) speed = 0.1f;

        mTTS.setPitch(pitch);
        mTTS.setSpeechRate(speed);

        mTTS.speak(text, TextToSpeech.QUEUE_FLUSH, null);
    }

    @Override
    protected void onDestroy() {
        if (mTTS != null) {
            mTTS.stop();
            mTTS.shutdown();
        }

        super.onDestroy();
    }
}