Kasm Workspaces has been machine translated into 91 languages. When a user hits Workspaces it will automatically set the language to match what the user has set in their browser preferences.
If you want to manually change the language that can be done by going to your User Profile / Settings and updating the Kasm UI Language dropdown.
?lng=<countrycode> before the # in the url, for example
https://server_or_ip/?lng=en#/dashboard will also work.
Please understand that machine translations are never perfect, if you want to help with the translations the top languages are managed at crowdin