I think legacy SW should move to UTF8 finally, if-possible (development-time-budget wise)...

If it is not maintained any more, you can use old binaries for some time.

I'm not even sure how much dev effort it can take to migrate legacy code to UTF8, sounds to me like it should require just few text resources files conversion, setting UTF8 encoding for app environment, and finding string related code operating with byte = single letter assumption (if the legacy app was text editor, this may be problematic, otherwise you may have none such place in source = no work).

Sounds to me like for many apps this migration is 1-4h task + testing/bugfixing. Maybe 1-2 days in relaxed way.