C++ has (albeit only since version 14) the single quote as digit separator, which is (IMHO) a better choice: https://en.cppreference.com/w/cpp/language/integer_literal
I know C++ added it 14 years after D :-) but I'm curious why you say ' is a better choice? I never read the papers proposing the feature, but the _ hasn't caused any problems for us, and I like it better myself.
Also, I'm glad and honoured to have a comment like yours in my history. Sorry for late reply.