The test booklet says the test are in English. but it is obvious from the arrests following crashes, that the language requirement in CA is not being enforced.
https://www.dmv.ca.gov/portal/file/california-commercial-driver-handbook-pdf/
I was at the DMV a few months ago and the CDL study guide was available in several languages.
Years ago, when I added an endorsement, I had to select English for the test.