I don't know if you can use multiple files per
language , but enum values can be translated this way:
&{myLangEnum}
and the messages file looks like
uk =
United Kingdom
fr = Royaume Uni
if this does not work try
&{myLangEnum.getName()}
you can use prefixes, too:
&{"langCode_" + myLangEnum}
langCode_uk = United Kingdom
greets,
Marcel