An offline translator for Windows

What runs on your computer

The translations come from Opus-MT, a family of translation models trained by the University of Helsinki's language technology group and published under the CC-BY 4.0 license. Each model translates one way between two languages, for example Spanish to English. Octoolo runs them with ONNX Runtime on your processor, the same engine its photo tools use.

• One download per direction. Each is about 105 to 130 MB, downloaded from Hugging Face once, checked against its fingerprint and kept in Octoolo's folder.
• Through English when needed. Most models go to or from English. Spanish to German, for example, uses Spanish to English and then English to German, so it needs both downloads.
• No account, no character limit. There is no daily quota and no server to queue on: the only limit is your PC's speed.

The panel's Languages button lists the languages on your PC, with Remove for one you no longer need. A removed language downloads again the next time you need it.

The languages

Into and out of English: Arabic, Chinese (simplified characters), Czech, Danish, Dutch, Finnish, French, German, Hungarian, Indonesian, Italian, Portuguese, Russian, Spanish, Swedish, Ukrainian and Vietnamese.

Into English only, for now: Hindi, Japanese, Korean, Polish, Thai and Turkish. The To list shows them greyed out under Only into English for now, because no model good and small enough to download exists yet for the other direction (one for English to Hindi was tried and made too many mistakes).

Any two of these languages can be paired through English, for example French to Spanish or Korean to German.

How good the translations are

Opus-MT models are much smaller than the systems behind online translators, so set your expectations accordingly. On everyday sentences, emails, instructions and articles they usually give a clear, faithful translation. They are weaker on slang, idioms, very long sentences and specialist terms, and a pair that goes through English can lose details such as formal and informal "you".

The models translate sentence by sentence, so the panel cuts your text into sentences and puts it back together with your paragraphs, indents, bullets and numbered lists as they were. Lines without words, such as numbers, dashes or web addresses, are left alone.

Machine translation makes mistakes. For a contract, a medical text or anything published, have a person who knows both languages check it.

Why offline

Text pasted into a website is sent to its servers. That is a problem for work emails, customer messages, medical or legal letters and anything under a confidentiality agreement. Here the text never leaves the computer: no connection is made while translating, and nothing is logged. It also works where there is no internet, on a train, a plane or a locked-down network.