People didnt just "give" their language to others willingly. People were killed over culture clash.
When you take a item belonging to a culture to which you are not apart of nor have familarity with the relations there, to them, yes, you are stealing.
Best example I can give (personal experience) is Deaf (not deaf) Culture.
Deaf Culture Hijacked: The Hearing-Minded Taking Advantage of the Word “Deaf”
deaf-someone with hearing lost
Deaf-Someone Deaf or Hard of Hearing who recognize herself by cultural identity with people like herself-hard of hearing and Deaf based on like experiences, art, language rather than hearing loss.
A lot of hearing are stealing the ASL language without using it within the Deaf community with which the language is owned.
ASL is part French as well as other signed languages. That doesnt change who can use it. It wasnt a choice.
Same as other languages. Some languages and some words in spoke langusge as well, is more appropriate spoken by the people who know the original dialect before it was mixed.