There was another native species to Vinsoth besides of the Chevins: The Chevs, who had their own language. However, the Chevs were slaves to the Chevins, and the Chevins forced their Chev slaves to learn Chevin language (usually they also made them learn Basic). Thus, the Chevin language was spoken by both Chevs and Chevins, while Chev language was spoken only by the Chevs.
As all the Chev speakers were familiar with the Chevin language, the Chevin language had a great influence on the Chev language.
Of course, Chevins traveling through the galaxy also learned to speak Basic.