Offline translation: what works without a signal, and what doesn't

When you lose your signal, Piou keeps translating the messages that are already on your phone, and Face to face mode keeps working, as long as you downloaded your languages ahead of time. Sending or receiving messages and making calls, on the other hand, require a connection. So the real work happens before you go: a few minutes on Wi-Fi.

What works with no signal

• Reading and translating messages you've already received. A message that reached your phone before you went offline is translated on the device, no connection needed, once the languages are downloaded. The "Translated" label and "Show original" work as usual.
• Face to face mode. Set the phone between you and the other person; it detects who's speaking, shows the translation and reads it aloud. One phone is enough, and the other person doesn't need the app.
• The web app, which keeps its interface and translation models cached.

Message translation and Face to face are part of Piou Premium.

What doesn't work with no signal

• Sending and receiving messages, including photos, voice messages and documents.
• Making or taking audio and video calls, which also means no translated subtitles, since they only run during a call.
• Anything that goes out to other people: posting a status, sharing your location, voting in a poll.

There's a simple reason. Messages are stored on our servers, in their original language, so they can be delivered and synced across devices; without a connection, they can't go out or come in. Calls connect two devices over the internet.

Why translation itself works offline

In Piou, translation happens on your device, never in the cloud:

• on iPhone, with Apple's built-in translation (Apple Translation, iOS 18 or later);
• on Android, with Google's ML Kit, whose models are downloaded to the phone;
• in the web app, with the open-source Bergamot engine and Firefox Translations models, or with Chrome's built-in translation on desktop where it's available.

Once the models are on your device, translating doesn't need a network. And translations never leave your phone: they aren't sent to our servers.

Your pre-trip checklist

1. Check your language in Settings → Language & translation.
2. Download the languages you'll need: yours, plus those of the people you'll talk to. It's a one-time download; do it over Wi-Fi if you can.
3. Open your important chats while you're still online, so the latest messages have actually reached your phone.
4. Test in airplane mode: one Face to face sentence, one message you've already received. Better to catch a missing language at home than at the arrivals hall.
5. Using the web app? Open it at least once while online, then install it: on iPhone, Safari → Share → "Add to Home Screen"; on Android, Chrome → ⋮ menu → "Install app."
6. Pack a power bank: Face to face uses the microphone and speaker.

Prepare a few key things in writing

Face to face works best with short sentences, and some information is safer shown than spoken. Before you lose your connection:

• Get your accommodation's address in the local language, written by the hotel or your host, and keep a screenshot. Showing an address to a driver beats dictating it.
• Carry allergies or medical needs on a card in both languages, translated by a bilingual person or a professional, not by an app.
• Think through the sentences you'll need first: "I'd like to go to this address," "How much is it?", "Where is the nearest pharmacy?" Short, literal sentences translate more cleanly.
• Save the local emergency number somewhere you can find it without a signal.

Three situations where this matters

On a long flight

Before boarding, let the messages from whoever is meeting you come in: you can reread and translate them in the air. Then get Face to face ready for landing, before you have a local SIM or Wi-Fi: the taxi line, the rental counter, the hotel front desk.

On a road trip through rural areas

Coverage comes and goes. Face to face still works at a roadside market, a guesthouse or a small-town garage. For messages, use the moments when you have signal to send what matters, in short sentences, and to pick up replies.

Traveling without a data plan

Plenty of travelers skip roaming and hop between hotel and café Wi-Fi. Face to face keeps working in between, at restaurants, pharmacies and taxis. For messages and calls, you'll need to wait for the next network.

Limits worth knowing

• Speech recognition depends on your device and what it supports for each language. That's why the airplane-mode test matters.
• Offline doesn't mean error-free. Machine translation still trips over humor, idioms, names, spoken numbers and messages that mix two languages. Confirm amounts in writing.
• For medical, legal or money matters, check with a professional or an interpreter. In an emergency, call the local emergency number from your phone: Piou doesn't call regular phone numbers, and its calls need a connection anyway.

What it costs

Messaging is free, with no time limit. Message translation and Face to face are part of Piou Premium, which starts with a 7-day free trial: a payment card is required, nothing is charged for 7 days, and then the subscription starts automatically unless you cancel before the trial ends. In the United States, Premium costs $5.99 a month or $47.99 a year; in the United Kingdom, £4.99 a month or £39.99 a year. Prices are adapted to your country and shown in your currency before you subscribe.