Yeah, it probably would be easier to run the English client. Even though HonorBuddy dumps known spells to the log at startup to give you a head start, there's all those aura checks, and those AREN'T dumped.
If I had one giant database of spell-ids, including aura-ids, to their English equivalent, I could work something up. But I wouldn't be able to test it, not having foreign language support on my lame low-end Windows 7 operating system.
It would work something like this: Instead of looking up the spellname by name, it would look up the spell id from the dictionary of English-to-ids. Then, it would get the spell directly by ID, and call that.
You've 'almost' got that right now, with the Spell_Overrides.txt file. For all spells in that file, FTW makes no attempt to look it up by name - it looks it up by spell ID. But, it doesn't have all the spells, and it doesn't accommodate German aura names, either.