Grammatical Mistake
The problems with the German strings have been fixed. I have also updated the FreeCol wiki page to improve the explanation for the tag syntax. The overall problem still remains, tho. A general bug report has been filed here: https://sourceforge.net/p/freecol/bugs/3303/
Freecol is smart enogh to allow each language to define themselves the "tags" they need to additional distinctions (e.g. tags like "people", "nation", "adjective"...), so nothenig really prohibit adding other grammatiacl distinctions (more than jsut those supported by "plural" rules, includnig the possibility to add tags for derived terms depending of grammatical gender, grammatical case, or how to prefix a definite or indefinite article, with possible elision or gluing as affixes).