Flutter Templates

How to Build an AI Voice Translator App Using Flutter and Back4App

30min

Introduction

In this tutorial, you will learn how to build an AI Voice Translator app using Flutter as the frontend framework and Back4App as the backend service. The app will allow users to translate speech, text, and images across multiple languages. It will feature AI-powered translation, optical character recognition (OCR), and speech recognition functionalities. By the end of this tutorial, you'll have built an app that can handle real-time translations and store history on Back4App for future use.

Prerequisites

To complete this tutorial, you will need:

  • A Back4App account. Sign up for a free account at Back4App.
  • Flutter SDK installed on your local machine. Follow the official Flutter installation guide.
  • Basic knowledge of Dart and Flutter. If you're new to Flutter, review the Flutter documentation before proceeding.
  • An account with a Translation API provider like Google Cloud Translation or DeepL.
  • Familiarity with REST APIs and asynchronous programming in Dart.

Step 1 — Setting Up Your Back4App Backend

In this step, you will set up a Back4App application, define the data models, and configure the backend to store translation history, languages, and user data.

1.1. Create a New Application on Back4App

  1. Log in to your Back4App dashboard.
  2. Click on "Create new App".
  3. Enter an App Name (e.g., "AI Voice Translator") and select your App Icon.
  4. Choose your server location if prompted.
  5. Click "Create".

1.2. Retrieve Application Keys

  1. Navigate to App Settings > Security & Keys in your app's dashboard.
  2. Note down the Application ID and Client Key. These will be required for the Flutter app configuration.

1.3. Define Your Data Models

We will create the following classes in Back4App:

  • User (default)
  • Translation
  • Language
  • Phrase
  • DictionaryEntry

1.3.1. Create the Translation Class

  1. Go to Database > Browser.
  2. Click "Create a class".
  3. Choose "Custom" and name it Translation.
  4. Click "Create class".

Add the following columns to Translation:

  • user (Pointer<_User>): Points to the User object.
  • sourceLanguage (String): Source language code.
  • targetLanguage (String): Target language code.
  • sourceText (String): The original text to translate.
  • translatedText (String): The translated text.
  • translationType (String): Type of translation (voice, text, image).
  • timestamp (DateTime).

1.3.2. Create the Language Class

  1. Repeat the steps to create a new class named Language.

Add the following columns to Language:

  • name (String): The name of the language (e.g., "English").
  • code (String): ISO code of the language (e.g., "en").
  • flagIconUrl (String): URL of the flag image representing the language.

1.3.3. Create the Phrase Class

  1. Create a class named Phrase.

Add the following columns to Phrase:

  • category (String): The category of the phrase (e.g., "Greetings").
  • sourceLanguage (String): Source language code.
  • targetLanguage (String): Target language code.
  • sourceText (String): The original phrase.
  • translatedText (String): The translated phrase.

1.3.4. Create the DictionaryEntry Class

  1. Create a class named DictionaryEntry.

Add the following columns to DictionaryEntry:

  • word (String): The word being defined.
  • language (String): The language of the word.
  • definition (String): The word’s definition.
  • examples (Array): Example sentences using the word.

1.4. Set Class-Level Permissions

Ensure that only authenticated users can access their own data:

  1. For each class, go to Security > Class-Level Permissions (CLP).
  2. Set the CLP to allow read/write access only to authenticated users.

Step 2 — Initializing Your Flutter Project

In this step, you'll set up a Flutter project and configure it to connect to Back4App.

2.1. Create a New Flutter Project

Open your terminal and run:

Bash


Navigate to the project directory:

Bash


2.2. Add Required Dependencies

Open pubspec.yaml and add the following dependencies:

YAML


Run flutter pub get to install the packages.

2.3. Initialize Parse in Your Flutter App

Create a new file lib/config/back4app_config.dart:

Dart


Replace 'YOUR_APPLICATION_ID' and 'YOUR_CLIENT_KEY' with the keys from Back4App.

In lib/main.dart, initialize Parse:

Dart


Create lib/app.dart:

Dart


Step 3 — Implementing Text Translation

The first feature to implement is basic text translation.

3.1. Configure Translation Service

Create lib/services/translation_service.dart to manage interactions with a translation API (Google Cloud Translation API or DeepL).

Dart


3.2. Implement Language Model

Create lib/models/language.dart to represent supported languages.

Dart


3.3. Create Text Translation Screen

Create lib/screens/text_translation_screen.dart to handle text input and translation:

Dart


Step 4 — Implementing Voice Translation

In this step, you'll add voice translation by integrating speech-to-text and text-to-speech functionalities.

4.1. Set Up Speech Recognition

Create lib/services/speech_recognition_service.dart using the speech_to_text package:

Dart


4.2. Add Text-to-Speech (TTS)

Create lib/services/tts_service.dart using the flutter_tts package:

Dart


4.3. Create Voice Translation Screen

Create lib/screens/voice_translation_screen.dart to handle voice translation:

Dart


Step 5 — Implementing Image Translation (OCR)

5.1. Set Up OCR Service

Create lib/services/ocr_service.dart using the google_ml_kit package:

Dart


5.2. Create Image Translation Screen

Create lib/screens/image_translation_screen.dart to handle image input and OCR:

Dart


Step 6 — Translation History and Phrase Book

In this step, you'll implement saving translation history and managing a phrase book.

6.1. Save Translation History

Update lib/services/translation_service.dart to save translation history in Back4App:

Dart


6.2. Implement Phrase Book

Create lib/screens/phrase_book_screen.dart to manage common phrases:

Dart


Conclusion

By following this tutorial, you have built a feature-rich AI Voice Translator App with Flutter and Back4App. You implemented:

  • Basic and advanced text translation.
  • Voice-to-voice translation using speech recognition and text-to-speech.
  • Image-to-text translation using OCR.
  • Translation history management and a phrase book for common expressions.

Next Steps

  • Enhance UI/UX: Improve the app’s interface for a smoother user experience.
  • Improve Error Handling: Add error handling and fallback mechanisms for API failures.
  • Implement Offline Mode: Cache common translations, phrases, and history for offline access.
  • Deploy the App: Prepare the app for deployment to iOS and Android platforms.