YouTube Subtitle Word Translator od Pavel

YouTube Subtitle Word Translator lets you learn languages while watching YouTube. Click any word in the subtitles/captions and see its translation in a tooltip — no need to pause, switch tabs, or copy-paste into a separate translator.

Features:

Click-to-translate individual words directly in YouTube's caption track
Choose your subtitle source language (or let it auto-detect) and your target translation language
Works with 14 languages including English, Russian, German, French, Spanish, Italian, Portuguese, Polish, Ukrainian, Turkish, Chinese, Japanese, Korean, and Arabic
Pick your translation provider: Google Translate (free, no setup), DeepL (free or Pro, API key required), LibreTranslate, or your own self-hosted/custom endpoint
Settings UI available in English and Russian

How it works:
Turn on YouTube's captions as usual, then click any word in the subtitle line. A tooltip pops up with the translation. Configure your preferred provider and languages from the extension's settings page.

Privacy note:
The word you click is sent to your selected translation provider (Google/DeepL/LibreTranslate/your custom server) to be translated — that's the only data this extension transmits, and only when you actively click a word. If you use DeepL or a custom endpoint with an API key, that key is sent along with the request to authenticate you with that service. No data is collected or sent anywhere else.

Source code: https://github.com/pvarenik/youtube-subtitle-translator