refactoring(serializers): move error messages from variables and add translation

[MiloLug]

Error messages moved directly to the error instead of the variables.
Invalid value translation added.

[iMerica]

I tried to fix your conflict, but pushing for maintainers is disabled on that git remote.

[merwok]

Out of curiosity, why move the error messages from variables?
It’s a style I use often in my own validation code, gives more room to write the message and avoids the delimiters salad of ({...: [_("...")]})