I am 👎 here. To me this is not a bug fix. By the way, we merged something like this with #25295 as a new feature for Symfony 4.1.

Same as @xabbuh

Sorry, I have not seen #25295 before.
I think it's a bug because we can use constants in yaml file since 3.2 but we can't use it in translation files.

It never worked, it's just unsupported. Not a bug but a missing feature really, which we would have preferred to add when introducing the constant, sadly nobody thought about it before.

Closing for the reasons explained by @xabbuh and @chalasr