You will get information via post and can select preferences of languages, but these are not guaranteed. DS1 listed Spanish and French, but was allocated French and German. DS2 listedSpanish and French, but was given Spanish and German. You can't change these as the whole form will do the same languages. Language 1 for the first half of the year and language 2 during the second half of the year. They start languages from scratch and my boys have had no issues.
The forms are divided depending on the languages they are taking. So if your DS has a buddy he wants to be in the same class as they need to request the same languages.