Sluka by Oskar Öster

Sluka marks the words you don't know yet on any page you read, in the language you're learning. Hover a word for its meaning, from a dictionary stored on your computer. Mark it known and it stops lighting up, everywhere.

What it does
- Works on news sites, blogs, Wikipedia and any other page
- Imported EPUB and PDF books, with the same marking
- Subtitles on YouTube and Netflix, read the same way
- 20+ languages, with offline dictionaries built in
- Counts how much you read and listen, per language

What leaves your computer
- Words and sentences you translate go to Google Translate
- Only if you add your own key: AI checks via OpenAI, Gemini or ElevenLabs
- The scoreboard and chat are optional and off until you say yes

No account. No tracking. Your word list stays in the browser.

Price
Free up to a set number of saved words per language. After that, a one-time licence from sluka.app lifts the limit. No subscription.

Coming from Chrome or Brave? Back up there to Downloads/Sluka, then use "Read from a folder" in Firefox. Your words, books and media come along.