Yes I know about Linguistics but I mean Language in itself removed from human context and simply existing as a structured form of communication.Don't know the exact definition of science, but I think the term ''science'' can apply to any system that tries to gather and evaluate knowledge.
As a personal rule of thumb, I consider any -logy, -nomy or -istics a science, as long as it is actual science, not peudoscience like astrology. (Not to be confused with astronomy.) And yes, in this sense language can be the subject of a science too: Linguistics, the study of language, and semantics, the study of the meaning of words.
Ironically enough, the definition of science has been discussed by philosophy for a long time.
Normally the way things can be classified as science is if the scientific method can be applied to them. That is, can you create theories and empirically(very important) test them and perhaps also make new discoveries? Don't really see that be applied to philosophy.