Some learners watch English videos with two lines of subtitles: one in English and one in their own language. Is this good for learning new words? In one study, 112 learners watched a short documentary. The two-line group remembered word meanings well.

But their eyes stayed mostly on the line in their own language. People who looked longer at the English words learned more. So when you see a new word, look at the English line.

Many learners now watch English videos with bilingual subtitles, showing English and their first language at the same time. In a 2022 eye-tracking study, 112 Chinese learners of English watched a documentary with bilingual subtitles, English captions, Chinese subtitles, or no subtitles. The bilingual group did better than the caption group on choosing word meanings and better than the Chinese subtitle group on recalling meanings.

However, they spent more time reading the Chinese translations than the English words, and they were worse than the caption group at recognizing the written form of new words. Learners who looked longer at the English words learned more. Other studies suggest a useful order. First, watch with first-language subtitles to understand the story, and then watch again with English on the screen.

Bilingual subtitles, which display English and the viewer's first language simultaneously, have become popular among learners who stream foreign series. Intuitively, they seem to offer the best of both worlds, with instant access to meaning and constant exposure to English spelling. An eye-tracking experiment published in 2022 put this intuition to the test with 112 Chinese learners of English, who watched a documentary under one of four conditions.

Those with bilingual subtitles outperformed the caption group in recognizing meanings and the Chinese-subtitle group in recalling meanings, yet they fell behind the caption group in recognizing the written forms of unfamiliar words. Their eye movements help explain this. Viewers spent longer on the Chinese translations than on the English targets, and only attention to the English words predicted learning.

So the first-language line acts as an easy shortcut that pulls attention away from the language being learned. A meta-analysis of 49 experiments confirms that English captions alone have a medium effect on vocabulary learning, while smaller studies suggest that presenting first-language and English text in sequence, rather than simultaneously, may work better. Because most participants were Chinese speakers watching short clips, these findings need testing with other learners and longer viewing.