If you learn a language with YouTube, a dual subtitle extension is usually the first thing you install: the original line and its translation stacked together, so the sentence you missed is one glance away. There are plenty of them and they look alike. The differences are in a few places:
- whether it also works on Netflix and other sites;
- what it does when a video has no captions;
- whether you can look up a new word on the spot and save it for review;
- whether it is open source, which browsers it runs in, and what costs money.
Below we go through seven common extensions on those points. We make Read Frog, so it comes first. Everything about the others comes from their own websites, help docs, store listings or GitHub, checked in October 2026. These extensions change often, so check each one's site before you install.
At a glance
| Extension | Beyond YouTube | No captions | Look up and save words | Open source |
|---|---|---|---|---|
| Read Frog | X, Netflix | AI transcription (Pro) | Click a word; review saved words with FSRS | ✓ |
| Language Reactor | Netflix | Speech recognition (Pro) | Click a word; full word saving needs Pro | No |
| Immersive Translate | Netflix and more | AI subtitles (Pro) | Selection translation; saving words not mentioned | No |
| Trancy | Netflix, Disney+ and more | AI subtitles (Premium) | Hover lookup, saved words, flashcards | No |
| InterSub | Netflix, Prime Video and more | Not supported | Hover lookup, wordbook, Anki | No |
| Dualsub | Viki, WeTV and more | — | — | No |
| BilingualTube | None | — | None | ✓ |
"—" means neither the official site nor the store listing mentions it. Supported browsers are listed in each extension's section below.
1. Read Frog
An open-source browser extension that puts video subtitles, web page translation and selection translation in one place. Words you meet while watching can be saved and turned into flashcards.
- Where it works: YouTube videos, Shorts and YouTube players embedded on other sites; videos on X (Twitter); shows on Netflix.
- Subtitles and translation: translates the video's own captions with the free Google or Microsoft translator, an LLM such as OpenAI, DeepSeek or Gemini, or a local model through Ollama. For videos without captions, AI can transcribe the audio and then translate the result.
- Learning as you watch: the video pauses while your pointer is on the subtitles. Click any word in the original line and an AI dictionary explains it in the context of that line, or swap in an AI action you wrote yourself. Save the result to your Notebase, add a card template, and reviews are scheduled with the FSRS algorithm. There is also AI smart segmentation, a full transcript of the video and an AI summary.
- Open source: yes, GPL-3.0.
- Price: translating captioned videos is free; AI transcription needs Pro or Ultra.
- Browsers: Chrome, Edge, Firefox.
A good fit if you want watching, reading and vocabulary review in one extension. The details are on Dual Subtitles for YouTube.
2. Language Reactor
A long-standing language learning extension that adds dual subtitles and study tools to the Netflix and YouTube players, plus a website where you can import articles and books to read.
- Where it works: Netflix, YouTube.
- Subtitles and translation: the free plan uses the subtitles the platform provides. Pro adds speech recognition for Netflix audio tracks, enhanced speech recognition on YouTube, and machine translation.
- Learning as you watch: click a word in the subtitles for its definition; there is also Lexa, an AI dictionary. Saved words come back in PhrasePump, a listening drill. On the free plan you can only save words inside PhrasePump; saving them elsewhere and exporting to Anki need Pro.
- Open source: no.
- Price: free plan plus a Pro subscription with a free trial.
- Browsers: Chrome only, on desktop.
A good fit if you mostly watch Netflix and already use Anki. See Read Frog vs Language Reactor for a full comparison.
3. Immersive Translate
Best known for bilingual web page translation. It covers web pages, PDFs, video and images, and also has iOS and Android apps.
- Where it works: YouTube, Netflix, and video and course sites such as Prime Video, Coursera and Udemy.
- Subtitles and translation: translates the video's own subtitles; for videos without subtitles, AI can generate them on Pro. It offers many translation services, including ChatGPT, DeepL, DeepSeek and Gemini.
- Learning as you watch: selection translation and hover translation. Its site does not mention saving words, review or flashcards.
- Open source: no. An early open-source version was archived in 2023.
- Price: YouTube bilingual subtitles are on the free plan; features such as exporting YouTube subtitles need Pro.
- Browsers: Chrome, Edge, Firefox, Safari.
A good fit if you mainly translate web pages and documents and want dual subtitles on the side. See Read Frog vs Immersive Translate for a full comparison.
4. Trancy
A video-first language learning extension, with mobile apps and a desktop app as well.
- Where it works: YouTube, Netflix, Disney+, TED, Coursera, Udemy and more.
- Subtitles and translation: translates the platform's subtitles, with Google Translate on the free plan; you can choose other translation services, and paid tiers can use LLMs. For YouTube videos without captions, AI subtitles transcribe the audio on Premium.
- Learning as you watch: hover over the subtitles to look up words, save words and sentences (the free plan has a limit), and practise with flashcards. Saved items sync to its learning center, where reviews follow FSRS.
- Open source: no.
- Price: free plan plus Premium; AI subtitles, AI grammar analysis and video summaries are in Premium.
- Browsers: Chrome, Edge, Firefox, Safari, plus Brave and Arc.
A good fit if you watch across several video platforms and want to keep studying on your phone.
5. InterSub
A desktop browser extension with a web wordbook and a Telegram bot for review.
- Where it works: YouTube, Netflix, Prime Video, HBO Max, Disney+, Crunchyroll, TED and more, plus course sites such as Coursera and Udemy.
- Subtitles and translation: uses the player's own subtitle tracks, including YouTube's caption translations, for free. When there is no track in your language, its paid AI subtitle translator translates the original line. It does not create subtitles from the audio.
- Learning as you watch: hovering a word opens a pop-up dictionary and pauses the video. Words you look up are saved to your wordbook automatically; review them with spaced repetition in the Telegram bot, or sync them to Anki (syncing the whole wordbook needs a paid plan).
- Open source: no.
- Price: the free plan has unlimited dual subtitles without the AI subtitle translator, and a monthly cap on word lookups; there are also pay-as-you-go packs and Premium.
- Browsers: Chrome, Edge, Firefox.
A good fit if you watch on many platforms that already provide subtitles.
6. Dualsub
An extension that does dual subtitles and nothing else, with a simple interface.
- Where it works: YouTube, plus iQIYI (iq.com), Viki, Youku, WeTV and others. Its changelog shows Netflix and Disney+ support was dropped.
- Subtitles and translation: uses the video's own subtitles. AI translation runs on its own servers and needs an API key; there is a free quota, and prepaid packs after that. Its docs list English as the only source language.
- Learning as you watch: its site does not mention looking up or saving words.
- Open source: no.
- Price: the extension is free; AI translation is prepaid.
- Browsers: Chrome, Edge, Firefox.
A good fit if you only want dual subtitles on English YouTube videos and don't need study features.
7. BilingualTube
A small open-source extension that does dual subtitles on YouTube only.
- Where it works: YouTube only.
- Subtitles and translation: uses YouTube's subtitles, preferring YouTube's own translations when they exist and calling a translation service when they don't. Microsoft Translator works out of the box, or you can add your own OpenAI API key.
- Learning as you watch: none.
- Open source: yes, GPL-3.0.
- Price: free.
- Browsers: Chrome, Edge, Firefox, Safari.
A good fit if you want a lightweight, open-source dual subtitle extension for YouTube.
How to choose
- You just want to follow the video: all of them do that. For captioned YouTube videos, Read Frog, Language Reactor, Immersive Translate, Trancy, InterSub and BilingualTube all show dual subtitles for free.
- You want to learn words as you watch: look for on-the-spot lookup and a way to review what you saved. Read Frog, Language Reactor, Trancy and InterSub all have that loop; they differ in where the review happens: in the extension, on the vendor's website, in Telegram, or in Anki.
- Your videos often have no captions: pick one that transcribes audio, such as Read Frog, Immersive Translate, Trancy or Language Reactor. It is a paid feature in all of them.
- You care about open source and your data: Read Frog and BilingualTube are open source, with their code on GitHub.
- You don't use Chrome: Language Reactor is Chrome-only. On Edge, Firefox or Safari, check the browsers line in each section above.
FAQ
Can I run two subtitle extensions at once?
You can install both, but turn subtitles on in only one of them for a given video, or you will get two layers of subtitles on screen.
Can't YouTube translate captions by itself?
YouTube's auto-translate shows one language at a time. A dual subtitle extension shows the original and the translation together, which is what helps when you are learning. Some of these extensions also let you pick the translation service or look up words right in the subtitles.
Do any free extensions handle videos without captions?
Of these seven, the ones that create subtitles from audio are Read Frog, Language Reactor, Immersive Translate and Trancy, and all of them charge for it. In Read Frog, AI transcription needs Pro or Ultra.