Who is the god or goddess of language and people?

It depends entirely upon your pantheon, and what you mean by "language and people".

If you wish to know about language in terms of how it is a means of intellect, there are many Gods known for their intelligence such as Odin, Athena/Minerva, Hermes. For writing specifically, I tend to work with Thoth, the scribe.

In terms of people, there are many household Goddesses that look over families/towns/regions where they are held sacred, such as Isis, Bast, Brigid, and Rhiannon.

If you mean language & people together, like a culture, you would look to the patron of that particular region or tribe (Athena in Athens, the Deified Pharaoh or Emperor in Egypt or the Roman Empire, respectively).

O that last note, calling upon the head of the pantheon you, or your culture follow, may be the best way to symbolize inclusion of all.

In the end, just work with whatever deity feels right.