Usually this is used in a sentence, such as "we experienced a language barrier but managed to resolve the problem." This phrase means that the two people in the conversation speak different languages or don't speak each other's language well enough to have an easily understandable conversation. A barrier is like an invisible wall, in this case, between the two people ( although the word barrier is also used to mean a literal wall or something else which creates division between people, objects, etc.) I hope this helps you!