Classrooms has the ability to be translated into another language if a language file is provided for the other language. If there is no file for the user’s set language, it will return english.
Currently classrooms lessons supports 10 other languages (besides English):
French (fr), Spanish (es), Czech (cv), German (de), Swedish (sv), Italian (it), Dutch (nl), Danish (da), Russian (ru), and Portugese (pt)
You can set your language with the language API /language [two-character-code]