A Language Reactor alternative for what comes after the video
Language Reactor is excellent at one thing: making Netflix and YouTube easier to follow in another language. Two sets of subtitles, a pop-up dictionary, and controls to replay a line until you catch it.
What it does less of is the part after the credits roll. Spark is a web app that picks up there. It turns a YouTube video into a transcript you read alongside the video, keeps track of every word you met, and gives you practice using them.
Facts about other tools last checked October 2026. Sources are listed at the end of the page.
The short version
Language Reactor sits on top of Netflix and YouTube while you watch, with dual subtitles and quick lookups. Spark brings a YouTube video, an article, a PDF or an EPUB into its own reader, tracks each word from unknown to passive to active, and adds review and a chat about what you watched. Use Language Reactor for watching. Use Spark when you want the words to stay with you. Many people could use both.
Spark and Language Reactor side by side
| Feature | Spark | Language Reactor |
|---|---|---|
| Where it works | Its own reader, in the browser. Videos come in from YouTube through the Chrome extension | On Netflix and YouTube, inside the page, through its Chrome extension. Also a web app with a text mode |
| Video | YouTube. The video plays pinned above a transcript that follows along | Netflix and YouTube, with subtitles in two languages and playback controls for replaying lines |
| Reading | Articles, PDFs and EPUBs as well as video transcripts | Books and websites through its text mode |
| Word lookup | Tap a word for its meaning in that sentence, plus a short AI explanation | Pop-up dictionary on any subtitle word |
| Saved words | Each word is unknown, passive (you recognize it) or active (you can use it) | Saving words and phrases is part of Pro |
| Practice | Spaced repetition on the words you met in your own reading. Text chat about the piece you imported. Type or speak; replies are text | Saved phrases for review (Pro) |
| Price | Free plan. Core $12/mo or $99/yr. Plus $19/mo or $149/yr. 7-day Core trial, no card. | Free extension; paid Pro plan. Check its site for the current price |
Language Reactor details from its Chrome Web Store listing, its Pro mode page and its official forum, as of October 2026. Its Pro feature list comes from a 2023 forum post by the team and may have changed.
Where Language Reactor is strong
If you want to watch a Netflix series in Spanish tonight, Language Reactor is hard to beat. It works inside Netflix and YouTube, so you never leave the page. Dual subtitles let you check the meaning of a line at a glance, and its playback controls make it easy to loop a sentence you missed. The Chrome Web Store lists it at 2,000,000 users.
Its free version covers a lot. According to a 2023 post on its official forum, Pro mainly adds machine translations and the ability to save words and phrases.
Where Spark is different
Spark is built for the time after you watch. When you import a YouTube video, the whole transcript sits under the video in Spark's reader, with every word colored by where it stands for you: unknown, passive or active. You can scroll back through what was said, look up a word in its sentence, and see which parts of the video you already have.
Then you practice. Spark reviews the words you met with spaced repetition and opens a chat about the video, in your target language. You can speak your replies or type them. The chat answers in text for now; your listening practice still comes from the video.
Spark is also a reader for articles, PDFs and EPUBs, so the words you meet in a video and in a news story land in one vocabulary.
Who should stay with Language Reactor
- You mostly watch Netflix. Spark does not import Netflix.
- You want help in the moment, on the streaming site, with as little setup as possible.
- Dual subtitles are the main thing you need.
Who should try Spark
- You watch a lot of YouTube and want to keep the words you meet.
- You also learn from articles or ebooks and want one vocabulary across all of it.
- You want to talk about what you watched, so the words get used.
How Spark works, in three steps
- 1
Bring in what you want to read or watch
Import an article, a PDF, an EPUB, or a YouTube video with the Spark Chrome extension. You pick the material, so it is about something you care about.
- 2
Read it with help on every word
Tap any word for its meaning in that sentence and a short AI explanation. Spark keeps track of which words are new to you, which you recognize, and which you can use.
- 3
Practice the words you met
Review your own words with spaced repetition, then chat about the piece in your target language. Type or speak your replies. Spark answers in text for now.
Other tools people compare with Language Reactor
If you are choosing a video tool, these are worth knowing:
Trancy
Best for: bilingual subtitles across several video sites
A browser extension and mobile app that adds bilingual subtitles to YouTube and Netflix, and also lists HBO Max, TED, edX and Coursera.
LingQ
Best for: the widest range of sources and languages
A reader and lesson library in 40+ languages. Its browser extension imports articles, YouTube videos and Netflix episodes, and it tracks every word through four levels before it counts as known.
Readlang
Best for: low-cost reading help on any website
A web reader and browser extension that translates words and phrases on the page, with AI explanations and spaced-repetition flashcards. Premium is $6 a month or $48 a year.
Dreaming Spanish
Best for: hours of video made for learners, sorted by level
A library of videos entirely in Spanish, sorted into seven levels from superbeginner to native, that counts your hours of watching. A French version exists too.
Questions people ask
Can I use Spark and Language Reactor together?
Yes. They do different jobs. Watch with Language Reactor, and import the YouTube videos you want to study into Spark to read the transcript, keep the words and practice them.
Does Spark work with Netflix?
No. Spark imports YouTube videos, articles, PDFs and EPUBs.
How does Spark import a YouTube video?
Click the Spark Chrome extension on a YouTube video. It reads the video's captions in your browser and opens the video in Spark with its transcript. The video needs captions in the language you are learning.
Does Spark have dual subtitles?
Spark shows the transcript in the language you are learning and gives you the meaning of any word or phrase you tap. It does not show a full second subtitle track.
How much does Spark cost?
Free to start. Every new account gets a 7-day trial of Core with no card. After that, Core is $12 a month or $99 a year, and Plus is $19 a month or $149 a year.
Facts about other products were checked on their public websites as of October 2026. Prices and features change, so check their site before you decide. If something here is out of date, tell us at matt@learnwithspark.io and we will fix it.
Related
Import the next video you watch
Bring a YouTube video into Spark, read along with it, and keep the words you meet.
Start your free trialFree to start. No card needed.