There is no simple answer to this question. First you would most likely need a valid language slot in your current unit, or a unit requirement to speak a specific language for a specific mission. In mission-specific situations the Army usually assigns an interpreter because units cannot not usually provide in-house language skills. The best possible way to obtain a language skill is to reenlist for jobs skills that require language skills. I believe you could get better assistance by visiting the DLI Website and contacting them directly.
Express your interest in language training and provide relevant information such as you DLAB score and whether or not you are a native speaker of a non-English language.