[itsme]

Thanks Mike. That's not important at all for me. I'm completely happy with Scandinavian which works flawlessly.

So take you time. It's definitely a good idea to plan thoroughly to find a flexible solution that's easy to maintain for you. There are so many possibilities. As far as I know do re mi exists in different variants in France and in Italy, Roman numerals might be interesting for some guys, there's Dutch where they use Ges and Gis as in traditional German, but B and Bes (for B and Bb) ...
Sciurius uses a configuration file for chord localization in his chordpro reference implementation.

Btw: I don't understand why Czech handles m vs. mi for minor chords.
The "chord quality" is imho something different than the localization. It's not only major and minor, there's also dim, maj7 and so on. There are so many styles and conventions that I would recommend leaving that completely to the user. 
Please find attached an example from Roemer/Brandt "Standardized Chord Symbol Notation"

What I would like to have is the support of lowercase letters for chords and transposing. Some conventions use lowercase letters for minor chords. Furthermore (and more important for me): it would allow using lowercase letters for single melody tones similiar to ABC notation and transpose them correctly together with the chords.
But: using lowercase characters for chords is not mentioned in the current chordpro standard (whereas I came across programs that support lowercase chords). So, if you consider supporting lowercase chords, we should involve Sciurius in the discussion.