Watch YouTube on iPhone or TV with bilingual subtitles. Tap a word or phrase to define it. Star real moments to turn them into video flashcards. Become fluent on autopilot.
Paste a link, share from YouTube, or search in your native language. Submate finds videos in your study language and builds bilingual subtitles you can tap, highlight, and save.
Paste a YouTube URL, share directly to Submate, or type what you want to watch.
Dual subtitles sit beside the video in landscape mode, with word lookup and highlighting.
Star useful sentences and Submate turns the original audio and video into flashcards.
Most apps want you to study. Submate wants you to enjoy your evening how you already do — and learn anyway.
Play YouTube inside Submate with the video on the left and bilingual subtitles on the right. Paste a link or search in your native language when you need an idea.
See a word or phrase you want to remember? Tap once. Submate captures the audio and video, the source line, and the translation, and turns it into a video flashcard tied to the moment you first heard it.
Spend a few minutes each day reviewing what you saved. Submate uses the FSRS algorithm to surface each card right before you'd forget it — the fastest known path from "I just heard this" to "I'll remember this forever."
Pair with YouTube on Apple TV, Roku, Fire TV, Chromecast, or most smart TVs. Keep the video on the big screen while your phone shows synced bilingual subtitles.
Pair once with the YouTube app on your TV. Submate stays in sync, lets you tap words as they appear, and saves clips without covering the video everyone else is watching.
I originally built Submate for myself, a native-English student of Thai, a difficult and under-served language.
Drills don't teach you to follow a fast-talking native. Hours of content one level above your own does. Submate's job is to lower the wall between you and the YouTube you already wanted to watch.
A flashcard in Submate is a clip of a real speaker on a topic you cared enough to watch. That semantic attachment is what makes vocabulary stick — and what makes a real conversation comprehensible six months later. The real recording is necessary for you to be able to understand real people.
You already watch YouTube. Submate meets that habit where it happens: on your iPhone, on your TV, or wherever you find native speakers worth listening to. Just watch what you enjoy, immerse yourself in the language and culture, and drill flashcards for a few minutes a day.
Thai. Vietnamese. Indonesian. etc. Every mainstream app only optimizes for the most popular languages and neglects the rest. Submate works the same for every language — YouTube has content in every language, and Submate works with them all.
Submate turns real videos into comprehensible input first, then into video flashcards you review for a few minutes a day.
Tell Submate what you already know and what you are learning. It uses those languages for subtitles, search, and flashcards.
Paste a link, share from YouTube, search from Submate, or pair with YouTube on your TV when you want the big-screen version.
Study-language and native-language subtitles stay in sync while you watch. Tap or highlight words when something catches you.
One tap saves the sentence, translation, original audio, and video context from the moment you heard it.
Submate schedules what you saved so each sentence comes back right before you are likely to forget it.
If something here doesn't answer it, get in touch.
No. Submate is completely free, and the core experience will always be free. Down the line we may add an optional premium tier for features that cost real money on our side to run — higher-quality AI translations, native-language dubs, that kind of thing — but the main subtitle and flashcard flow stays free forever.
For listening and reading, yes — that's what Submate is optimized for, and you'll get there fast. Speaking is a separate skill that needs its own practice; no app replaces talking to humans. The fastest path I've found to all-around fluency is three things, in parallel:
Do those three together and you'll reach fluency in listening, reading, and speaking quickly. Handwriting is optional these days — speech-to-text on your phone covers almost all real-world typing (which is good, because for languages that use a script different from your native language, learning to write and type would otherwise add another two skills to learn).
Honestly, not really. Submate is built for intermediate and advanced learners — if you're starting from zero, you'd be limited to videos made for very small children, which isn't the kind of input that holds adult attention. Spend a few months on a vocab-focused beginner app first, then come back once you can roughly follow conversational content.
Effectively all of them. Submate works with any language YouTube has captions for — that's 100+ languages, including under-served ones like Thai, Vietnamese, Indonesian, Tamil, and Swahili.
Yes. Add as many study languages as you like from Settings — Submate keeps a separate flashcard deck, streak, and daily goal for each one.
Apple TV, Roku, Fire TV, Chromecast with Google TV, and most smart TVs (Samsung, LG, Sony, etc.) — anywhere the YouTube app supports the 12-digit "Link with TV code" pairing.
No. Submate works with regular YouTube on any device. Premium is nice for ad-free viewing, but Submate itself doesn't need it.
Only when you want to see Submate's subtitles on it. The TV pairing itself stays connected whether the phone app is open or not, but the bilingual subs render in real time on the phone, so for the dual-subtitle experience you'd keep the app open. Most people prop the phone on the couch or coffee table.
Not really. Watching needs YouTube on the TV (online by definition), and reviewing your saved cards needs internet too — the video clips stream from the cloud rather than living on your phone. Local caching of saved clips for offline review is on the roadmap.
Not yet — coming soon. iOS is first; Android is next.
A Chrome extension is on the roadmap. It'll ship after the Android app.
Soon. Anki-compatible export is on the near-term roadmap.
The minimum needed for the app to work and nothing else. We store your account (email + name from Google sign-in), the subtitles you actively starred, your review activity, and basic study stats. We do not track your YouTube watch history — Submate only sees the moments you tap to save. Translations and word lookups are fetched via OpenAI's API on demand and not retained beyond the request. We never sell or share your data.