Unless you master the language in real life, I don’t think so.
One day before the Konusma Yarismasi (a random language competition I attended in Istanbul), my Turkish teacher joked by saying: “If you really want to win tomorrow, make sure you dream in Turkish tonight.” At that time, stupid and naive, the young me laughed and didn’t take it seriously.
After some time, I stumbled upon articles which exposed researches done by smart psychologists and discovered that there really is a certain relation between language aptitude and your subconscious realm.
“Dreams present themselves as more than just a series of images. A dream need not to be a ‘silent movie’ or silent videotape; it may also include a ‘sound track’. While this sound track may contain all sorts of auditory impressions, it usually abounds in verbal material.” —Linguistic Aspects of Freud’s Dream Model
Evidences showed that apparently the language system is also active during your unconscious phase. Thus, you might actually refer to your dreams in checking whether you’ve achieved certain level of proficiency in a new language. Oh! Probably one day TOEFL and IELTS would require ‘dream-testing’ added to your final score!
Hence, should my mind have absorbed Turkish vocabularies and grammar rules well during the past month of trainings, it would easily be able to set Turkish as my ‘soundtrack’ that night. What happened back then? I did dream about having a chit-chat in Turkish. So, yeah!
Good luck paying more attention to the language you use when you dream.