Especially English grammar.
I can remember folk in my school French class being amused that the French spoke of trousers and diseases in the singular.
Anent diseases, it seems that we speak of the common ones that causes rashes and swellings in the plural, but others in the singular: measles, mumps, shingles and yaws but malaria, cholera, plague, etc.
Incidentally, the French for malaria is paludisme. I never thought about where they got that from until we cycled past an area called La Grande Palud in Brittany a few years back. It means "marsh".
Malaria might also mean a bad song, e.g. rap, which makes me feel ill.