In order for you to change Languages in CometChat. Please follow below mentioned steps.
Open CometChat Admin Panel on another tab and refer "Localize" section.
When you change dropdown value move to CometChat "Localize" section and refresh the page. you can see the changes in Language Listing.
Please refer Sample Example for the same
Once, the above mentioned steps are performed you would be able to see the changes in language as per your request.
Please do find the attached file for the same.