In the 1930’s, C. K. Ogden wrote a book on basic English in which he listed 850 words that would get you by if learning English as a second language.
Subsequent writers have suggested that you could use these words to learn any language. Translate them into French, for example, and you would know enough to get by in that language.
You could only be very basically fluent, with little capacity for writing and reading. But this is frequently the case with multi-lingual people. Communication may be manageable but culture is a bit ambitious.