Normalization isn't based on what language the text is. NFC just means never use combining characters if possible, and NFD means always use combining character

Normalization isn't based on what language the text is. NFC just means never use combining characters if possible, and NFD means always use combining characters if possible. It has nothing to do with whether something is a "real" letter in a specific language or not. The whether or not something is a "real" letter vs a letter with a modifier, more comes into play in the unicode collation algorithm, which is a separate thing.