Since I'm also in a "comma" country (same as haavarda) I've also experienced some dot/comma issues as the Indigo device states in general have dot/period rather than comma. It hasn't been a problem for me though, since Mac OS speech will pronounce 2.5 as "2 comma 5" when speaking Norwegian.
I was thinking in lines of having a text field in plugins config where users could enter a locale name, "nb_NO" for Norway and so on. And then have one additional state 'state.locale' for example. This would make it possible to have both thousand separators and decmial point correct for all countries. Best would be if this was possible in Indigo server of course. And I think matt or jay may have to comment on feasibility of using locale in a plugin, if this might break other things etc..
Another possibility is maybe to have a function included in a separate plugin with wrapper devices, such as the
Adapters plugin for example. It may very well be possible already using the custom formula adapter, although I haven't tried it.