Under Review in the bar above the path, Default language is either Auto-detect per person or English for everyone. Auto-detect writes to each person in their own language when it is one of the 23 below, the same on every step, and in English when it is not or cannot be told.
Each email step can also be set to one language in its Language card. The list covers 23 languages, including English, Spanish, French, German, Japanese, Chinese and Albanian.
Templates sent as designed go out in the words you wrote.