TranslationApp

Hindi ↔ English ↔ Marathi Android translation app

A full-stack Android translation project for Hindi, English and Marathi using a FastAPI backend, IndicTrans2 ONNX models and SQLite result caching.

Android source · Backend source · Report a bug

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Supported translations

• Hindi → English
• Hindi → Marathi
• English → Hindi
• English → Marathi
• Marathi → Hindi
• Marathi → English

The Android app includes source and target language selectors plus a one-tap swap button.

Architecture

Android app
   │
   │  POST /translate
   │  text + source_language + target_language
   ▼
FastAPI backend
   │
   ├── SQLite translation cache
   │
   └── IndicTrans2 INT8 ONNX
         ├── English → Indic
         ├── Indic → English
         └── Indic → Indic

Language codes used by the models:

Language	API code	IndicTrans2 code
Hindi	hi	hin_Deva
English	en	eng_Latn
Marathi	mr	mar_Deva

Features

Android

• Kotlin + Jetpack Compose
• Hindi, English and Marathi selectors
• Six translation directions
• One-tap language swap
• Retrofit API client
• ViewModel-based UI state
• Loading and error states
• Latency display
• Cache-hit indicator
• Configurable backend URL

Backend

• FastAPI REST API
• IndicTrans2 CPU inference through ONNX Runtime
• Automatic model selection by translation direction
• Lazy model loading to reduce memory usage
• SQLite translation cache
• Health endpoint
• Input and language validation
• Docker support

Translation models

The backend uses three INT8 ONNX model families:

• hari31416/indictrans2-en-indic-dist-200M-ONNX-int8
• hari31416/indictrans2-indic-en-dist-200M-ONNX-int8
• hari31416/indictrans2-indic-indic-dist-320M-ONNX-int8

Only the model needed for the current direction is kept active in memory.

Run the backend

cd backend
python -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt
uvicorn main:app --host 0.0.0.0 --port 8000

Then check:

curl http://127.0.0.1:8000/health

Example translation:

curl -X POST http://127.0.0.1:8000/translate \
  -H "Content-Type: application/json" \
  -d '{"text":"नमस्ते","source_language":"hi","target_language":"en"}'

See backend/README.md for backend details.

Run the Android app

The debug build defaults to:

http://10.0.2.2:8000/

To use another backend URL:

gradle :app:assembleDebug \
  -PTRANSLATION_API_BASE_URL=http://192.168.1.10:8000/

For production, use HTTPS.

Current limitations

• The first request for a model direction must download and initialize that model.
• Switching between English→Indic, Indic→English and Indic→Indic can require loading a different model.
• Translation quality should be reviewed before high-stakes or production use.
• The Android app requires a reachable backend.
• Models are not yet running directly on-device.

Roadmap

• Hindi ↔ English translation
• Hindi ↔ Marathi translation
• English ↔ Marathi translation
• FastAPI backend
• IndicTrans2 ONNX inference
• SQLite caching
• Loading and error states
• Android CI
• Add translation history
• Add speech-to-text
• Add text-to-speech
• Explore direct on-device inference

Contributing

Please read CONTRIBUTING.md before opening a pull request.

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Built by Aditya