RTranslator

RTranslator 2.1.5 is an Android app for people who want to translate spoken conversations without sending speech to a cloud service. It runs speech recognition and translation on the phone and works offline after an initial model download of about 1.2 GB. The app's code is open source under Apache 2.0, though it uses some closed-source components and its NLLB translation model has a non-commercial restriction.

Conversation mode connects phones over Bluetooth and translates speech in both directions. Each participant hears the translation through their phone's speaker or a Bluetooth headset. It supports conversations with multiple participants, so it isn't limited to a pair of phones.

For brief exchanges with someone who doesn't have the app, WalkieTalkie mode lets two people share one phone and take turns speaking. It recognizes which of the two selected languages a person speaks, translates their words, and reads the result aloud. This mode doesn't support Bluetooth headsets. There's also a text translator with copy and spoken playback controls.

Whisper handles speech recognition, while NLLB handles translation through ONNX Runtime. The app needs at least 6 GB of RAM and a sufficiently fast phone CPU for practical response times. Spoken output uses Android's system text-to-speech engine, which determines voice quality and available spoken languages. Use a TTS engine and voice packs that work offline for offline spoken playback.

The developer says the app doesn't collect personal data. In connected conversations, phones exchange transcribed text rather than sending it to a central server. Both voice modes can keep working in the background or with the phone on standby, though some phones restrict background processing.

The separate 3.0 beta changes translation models. Its Bergamot, Madlad and HY-MT options belong to that prerelease.