Kalix language is very much related to nearby languages/dialects westwards and southwards Råneå, Luleå, Piteå, Skellefteå, Umeå northwards Overkalix etc., basically mutually intelligible with Kalix language as they all are part of a broader Westrobothnian dialect continuum.
Ethnologue reports that it is mutually intelligible with Kwala, in the C.20 group where it was classified by Guthrie 1948.
They spoke the Hitchiti language, which was part of the Muskogean language family; it is considered a dialect of the Mikasuki language, with which it was mutually intelligible.