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Among all the language learning apps out there, Deja is one of the few that truly caught my eye — or rather, it finally did what I’d always hoped someone would do.

It doesn’t rely on “word memorization” or “drill exercises” to pile up knowledge. Instead, it builds around context-based learning, bringing language acquisition back to where it naturally belongs — in real, authentic content.

Deja’s logic is remarkably clear:

• Authentic content sourcing: Choose materials you’re genuinely interested in directly from YouTube, Bilibili, or podcasts.
• Layered language information: The system automatically generates subtitles, translations, and phrase breakdowns, while highlighting key expressions.
• Corpus building: Instantly save selected words, phrases, or sentences to your personal corpus with one tap.
• Flashcard review system: Saved content is converted into spaced-repetition flashcards to reinforce memory.

The whole process creates a seamless learning loop — from natural input → precise extraction → personalized review.

Compared with traditional language-learning apps, Deja’s biggest strength lies in how it systematizes fragmented content. In the past, when watching English videos on YouTube or Bilibili, we could only add new words to a dictionary or vocabulary app. If we wanted to capture the original context, we had to manually enter it — tedious, time-consuming, and hard to maintain. Now, Deja makes it effortless to turn every piece of authentic language material into something you can actually learn from and apply.

The way you receive contextual input is also fully customizable. Currently, Deja supports content from YouTube, Bilibili, and podcasts, allowing you to choose and learn directly from native videos and audio sources.

When it comes to subtitle generation and sentence segmentation, Deja gives you full flexibility. You can directly import the original subtitles from a video, or—if the video has none—use your credits to automatically generate them. On mobile, you can even generate subtitles offline using a local model without consuming any credits. The generated subtitles are not only accurate but also intelligently segmented by meaning, making later corpus organization and study much smoother.

Deja automatically detects key phrases and collocations within sentences, highlighting them to help learners quickly grasp authentic expressions. If needed, you can also manually select and save specific phrases or sentence chunks. Words you’ve previously saved will automatically appear highlighted in subtitles, allowing you to reinforce vocabulary across different contexts through repeated exposure.

What’s particularly impressive is that Deja also supports grammatical structure analysis for complex sentences. The system divides intricate sentences into logical chunks and labels syntactic relationships—identifying main clauses, subordinate clauses, adverbials, attributives, and more—then visualizes their hierarchical structure. This helps learners clearly see the logical flow and semantic focus of each sentence. It’s a feature especially valuable for intermediate to advanced learners aiming to strengthen their reading comprehension and writing skills, helping them move beyond the “knowing the words but not the sentence” stage.

Through this fully automated process, Deja breaks down the most tedious parts of English learning into a true “one-click” workflow, dramatically reducing the manual effort required in the early stages of study organization. You can even export your complete learning records as PDF files—perfect for archiving, printing, or periodically reviewing your progress over time.

For review sessions, Deja’s phrase library doesn’t just display the phrases you’ve saved—it also brings back the original context in which they appeared, including the source video, sentence position, and corresponding audio clip. This allows learners to easily recreate the original learning scenario, reinforcing both contextual understanding and long-term memory.

In its word library, Deja introduces the concept of “Word Families.” Each entry automatically includes all its common forms—such as nouns, verbs, adjectives, and adverbs—helping learners not only grasp the meaning of a word but also master its diverse usages. This design makes vocabulary learning more structured, multidimensional, and closely aligned with how language is actually used in real contexts.

Finally, let’s talk about Deja’s flashcard feature. It’s not about traditional rote memorization, but once again built around authentic language contexts. Based on the words, phrases, and sentences you’ve saved, the system automatically generates flashcards with their original contexts. During review, you don’t just see the meaning—you can revisit the very sentence and surrounding dialogue from the original video or audio where the expression appeared.

This design turns review into something far beyond mechanical repetition—it becomes a journey of context recall. When you see a phrase, you instantly remember where it appeared, what tone it carried, and in what situation it was used, subconsciously reinforcing your real-world language intuition.

Deja’s flashcard system also integrates a spaced repetition algorithm, automatically adjusting review frequency based on your memory curve. Content you’ve mastered appears less often, while words or sentences you’re more likely to forget are intelligently resurfaced. This approach makes memorization feel more natural and efficient, ensuring that every review remains anchored to authentic language experiences.

As someone who has repeatedly tried to learn English through watching shows and videos—only to give up because manually organizing learning materials was too tedious—I finally found a way to stay consistent. Deja makes the process flow smoothly and naturally: input → refine → review—a complete learning loop that eliminates the old “watch but don’t learn” trap.

From a product perspective, Deja feels more like a Language Learning Operating System (OS) than a traditional learning app. It transforms fragmented content into an integrated ecosystem, where every act of watching, saving, and reviewing feeds back into genuine progress. While many English learning apps offer example sentences or clips from movies, they rarely become your context. Deja’s brilliance lies in letting you build your language environment around your own interests, materials, and contexts.

The developer, Steve, continues to expand Deja’s features. Upcoming updates include text reading, shadowing practice, and support for multiple languages—which means Deja won’t just help you understand English, but also use it confidently, and even branch out to other languages.

After my experience, I immediately subscribed—and honestly, it’s the first time a learning tool made me want to write a full review out of sheer excitement. There’s still room for optimization, of course, but if you’ve been searching for a truly context-based approach to language learning, Deja is absolutely worth trying.

I sincerely hope that Steve and the Deja team continue to make it better and better.

Deja is now available on Web, Chrome Extension, iOS, and Android. The iOS China version is under review, but you can join the TestFlight beta program via the official website. The international App Store already offers the full release, and Android users can download the latest APK directly from Deja’s website.

Official Website: DejaVocab – Every Word You Encounter Counts