Demirline — YouTube Language Learning

Demirline turns YouTube into a language-learning tool. Watch any video with dual subtitles — original captions plus an AI translation side by side — look up words instantly and repeat sentences to train your ear. ★ KEY FEATURES • Dual subtitles: original + AI translation, sentence by sentence • Sentence repeat (press S) and auto-pause at sentence boundaries — perfect for shadowing • Word dictionary: click any subtitle word, or select text on any site (Alt+W), with pronunciation • Paragraph translation on any website: hover + Alt+T • Sentence translation on any website: select + Alt+S • 10 interface languages (auto-follows your browser language) • Smart translation engine with sliding window + persistent cache • 4 AI providers: OpenAI, Anthropic (Claude), Google Gemini, OpenRouter ★ PRIVACY Bring your own API key. Your key is stored locally in your browser and used only to call the AI provider you choose — nothing is sent anywhere else. Demirline is open source and free. Start learning with the videos you already love!