Bilingual Subtitles × Interactive Practice on YouTube / Bilibili / Netflix
Three content scenarios, one practice loop
Learn from Videos
Auto-extract subtitles from YouTube / Bilibili / TED / Netflix. 7 modes (shadowing, dictation, cloze) ready in one click.
Learn from Articles
One click on any BBC / NYT / Medium article to enter full-article learning: original + AI translation, 5 modes reused.
Learn from Snippets
Select any passage, pop a learning card: deep translation + contextual examples + one-click vocab save, cross-source unified.
"Learning a language isn't about memorizing rules, it's about immersive practice."
“学习语言不是死记硬背规则，而是沉浸式的实践练习。”
4 major video platforms + any web page
YouTube
SupportedNative subtitle extraction, multi-language switching, full compatibility with videos / Shorts / live streams
Netflix
SupportedOfficial TTML / DFXP XML & WebVTT subtitle stream real-time interception, seamless multi-language switching
Bilibili
SupportedWBI interception + multi-scenario adaptation for bangumi / movies / courses
TED
Supportedhls.ted.com direct subtitle push, full talk text + timestamp sync
Any Web Page
SupportedReadability content extraction + generic OCR fallback — articles, PDFs, and videos all learnable
5 skills in one loop
TTS sentence-by-sentence / sentence-level pause / complete dictation loop
Record + speech recognition + AI word-by-word scoring, 0.5x - 2.0x speed adjustable
Full-text extraction + AI bilingual comparison + saved vocabulary auto-highlighted in original
Word-by-word input / AI-generated dictation at your CEFR level / wrong words auto-enter the loop
Wrong words auto-enter SM-2 spaced repetition queue, CEFR vocabulary estimation
One sentence, five practice ways
Not 5 tools — 1 sentence, 5 practices. This is the biggest difference from Duolingo or immersive translators.
7+ practice modes, switch on demand
Wrong words auto-enter SRS — LangKey's moat
Practice
Any wrong / unfamiliar word from any mode is captured automatically
Store
Written to local vocabulary bank with context, source URL, and source platform
Review
SM-2 algorithm calculates next review time, push precisely
Learning Center: Your language growth dashboard
Today's Overview
Study time / practice completed / words due for review / streak days
SRS Review Panel
Today's due words + error set, filter by level / source / time
Error Analysis
Spelling / tense / preposition / meaning 4-category error stats, recommend targeted practice
Learning Calendar
GitHub-contribution-style streak visualization, motivation made visible
Frequently Asked Questions
Is LangKey free?
The core features — bilingual subtitles, tap-to-lookup, 7 practice modes and SRS review — are completely free on Chrome / Edge / Firefox, and the project is open source. Pro adds AI dictation, Anki two-way sync and a cloud learning center, with a 14-day trial.
Which platforms and browsers are supported?
Native support for YouTube, Netflix, Bilibili and TED, with generic OCR fallback for any web page. Works on Chrome, Edge and Firefox.
How do I set up bilingual subtitles (e.g. English-Chinese)?
After installing, open any video page — LangKey auto-extracts subtitles and renders high-contrast bilingual pairs. You can switch target language, font size and display mode (bilingual / original / translation) in settings.
Can I use Bilibili (B站) to learn a foreign language?
Yes. Bilibili's WBI subtitle API is natively integrated, so bangumi, movies and course videos all support bilingual subtitles plus shadowing / dictation / cloze practice.
Are my learning data uploaded anywhere?
No. All learning data is stored locally in IndexedDB and learning records are never uploaded; AI translation only sends the sentence / paragraph you are reading right now. The code is open source so you can audit it.