In large schools, lower-level intro classes can be huge (many classes with many students in each class), so there's usually an extremely standardized (and mecha

In large schools, lower-level intro classes can be huge (many classes with many students in each class), so there's usually an extremely standardized (and mechanized) curriculum that ensures everyone learns basically the same thing and labs and recitation sections are interchangeble. So when they switch languages, they mean moving all this curriculum to another language at once. The higher level courses don't change.