The Subconscious Power of Dreaming in Two Languages

Waking up from a dream in which you were speaking a language you hardly know can be unsettling. Speaking it fluently, confidently, and with the ease that never quite materializes during waking hours, rather than stumbling through it like you might at a café in Barcelona. It occurs more frequently than most people realize, and scientists are just now starting to figure out what it means.

For the majority of human history, or as long as people have spoken multiple languages, bilingual dreaming has been a phenomenon. However, serious research on it is still in its infancy. The mechanics of what happens when a multilingual brain goes into sleep have begun to be dissected by a small body of research, including studies from the University of Silesia and a sleep and memory lab at the University of York. The results are odd, sometimes poetic, and might be helpful to anyone attempting to learn a second language.

A study of twenty-two multilinguals who were asked to consider their dream languages yielded one of the more startling findings. While they were asleep, the participants were not merely passively exposed to foreign words. In some instances, they dreamed in languages they had only briefly encountered, conversed, and switched codes between languages mid-sentence. In the dream, a Croatian participant recounted attempting and failing to converse with a stranger in Italian, German, and English before both realized they shared Polish. They both laughed with relief. It’s a brief moment, but it sheds light on how the sleeping brain classifies and evaluates language knowledge—almost like performing diagnostics on a system it developed during the day.

Exposure appears to be the driving force behind these nocturnal language choices. A language’s likelihood of emerging during sleep increases with the amount of time spent hearing or speaking it while awake. However, exposure is not the only explanation. Emotional weight is also important. Regardless of a person’s current language, dreams about childhood typically arrive in the language of the child. A Thai-American woman had a dream of shopping for a dress for her deceased sister and discussing the option with her nieces in both Thai and English. It turns out that the brain does more than simply organize languages in alphabetical order. It arranges them according to emotion, location, and the first speakers.

Professor of psychology Gareth Gaskell, who oversees York’s sleep, language, and memory lab, has devoted years to researching how the brain assimilates new words while you sleep. Most people are surprised to learn that even adults learning their native tongue pick up about one new word every two days. When a new word is added to the system, it competes with previously stored words that sound similar. Gaskell cites the introduction of “Brexit” into the English language, which momentarily confused with “breakfast” in people’s minds and resulted in memorable blunders on live television. While you sleep, you sort out that competition and integrate new words with what you already know. During the day, the hippocampus rapidly takes in information, which is then transferred to other parts of the brain overnight for filing, cross-referencing, and tagging.

This tagging process is particularly interesting to bilingual speakers. Every word has a language label, and the brain learns to activate some vocabulary while suppressing others. Some of this suppression may be practiced in dreams, though this has not yet been demonstrated. The reasons why some languages predominate in dreams and why some people claim to speak languages they can hardly understand while awake are still largely unknown.

The anxiety that permeates many bilingual dreams is difficult to ignore. People talk about freezing in front of strangers whose language they don’t understand, frantically looking up words in dream dictionaries, and racing to catch trains between linguistic settings. These pictures are not arbitrary. Compressed and replayed in the dark, they reflect the actual stress of juggling multiple languages on a daily basis.

All of this suggests that sleep is doing far more linguistic work than anyone gave it credit for a generation ago, even if the science is still in its early stages. The subconscious mind is more than just a filing cabinet for vocabulary. It involves blending languages, assessing emotional ties, simulating social situations, and sometimes allowing someone who has never learned Japanese to speak it fluently. It remains to be seen if that is true language acquisition or more akin to cognitive rehearsal. However, the experience itself is sufficient proof that something significant is going on beneath the surface for the millions of people who wake up startled by a dream conversation in a language they thought they had forgotten.