Whenever Swift adds a new keyword, they just add it and break everyone’s code. They do provide migration tools in Xcode though.

C++ has had two-word keywords since the beginning, static_cast, dynamic_cast, etc.

What I truly don't like is C's propensity to add new keywords that begin with an underscore and an uppercase letter. Like _Bool, or _Atomic. (I know the rationale, these can't be used as identifiers due to UB, but it still looks weird to me.)

co_await is so bad that co_X has become a running joke in the C++ community.

I think non_sealed would be better than non-sealed though, because AFAIK there used to be no identifiers with hifen before.