It is indeed possible for some multilingual individuals to dream or think in two different languages at once or switch between languages without consciously realizing it. This phenomenon is known as "code-switching" or "bilingual language processing." Code-switching occurs when a person seamlessly incorporates elements of one language into another during their speech or thoughts.
In dreams, the same process can occur, where the brain may mix languages the person knows, resulting in a dream that incorporates both languages without the dreamer being consciously aware of it. Similarly, during deep thinking or intense thought processes, a bilingual person might find their mind switching between languages based on familiarity, comfort, or contextual cues.
The ability to dream or think in multiple languages simultaneously is more common in individuals who have a high level of proficiency in both languages or who have been exposed to multiple languages from an early age. It's worth noting that the experience of dreaming or thinking in multiple languages can vary among individuals, and not everyone who knows multiple languages will necessarily experience this phenomenon.