Solfege can easily be translated to your favourite language. The translated messages are stored in .po-files, like most GNU programs.
Translated messages Solfege give to the user is stored in the po/
subdir. To add a language, lets say the two letter code is nn,
you do:
LANGUAGES=no de nn
./configure && make && make install
All english html files is stored in online-docs/C/. Your german translation should go into online-docs/de/. Do not translate the file names.
Lessonfiles can be translated it two ways. Strings can be marked to be looked up in the message cataloges (.po-files):
name = _("Major")
Or you can include the translation in the lessonfile:
name = "Major"
name(no) = "Dur"
name(fr) = "Majeur"
Generally, for very common strings, like "major", "minor" etc, you can use .po-files, but for the rest, you should inlucde the translation in the lessonfile.
Do not mark chord names like 7 or m7-5 for translation using .po-files.