I don't think a team being fluent in the same language is that important. I think the main thing is sharing a common language with the manager. On the pitch basic instructions and changing to pre drilled routines and plans is the bulk of communication. Off the pitch, a much greater understanding during training is where the importance will lie, but that doesn't need to be done in one language if the manager is multi lingual. An example would be, someone teaching you how to operate a machine in a language you don't really speak, compared to someone asking you to operate a machine you already know how to use in a language you don't understand.