During my Python workshops I used Pythonic as good and Pythonesque as bad to instil in people a sense of being idiomatic and in sympathy with the language and underlying runtime. Maybe I was abusing the term Pythonesque, but it worked for the audience.
The languages you mentioned are all old languages and suffer from style wars and thus doubt and uncertainty. Also a lot of poor code. Languages such as Go, Rust, Ceylon, etc. try to encourage (well Go totally enforces) a single style of code that everyone will use. This avoids style wars. Also as a side effect it makes it a lot harder to write non-idiomatic code. This I think is a good thing. Whilst I have lots of disagreements with the one-and-only Go format style, that there is only one removes a whole collection of decisions a programmer has to consider. So Go removes a whole dimension of style, and thus a whole dimension of idiomatic.
Anyway, in one sense you are totally right “idiomatic” serves for all languages. It is nice though that “idiomatic Python” can be shortened to Pythonic.