Yes, my lang file is not new 
but that modify was only about recognizing .pde files under gedit, and it had a "cohabitation" problem with c.lang file 
I fixed the problem and included some arduino keywords.
I have no particular experience under my belt I just opened various .lang file and tried to understand what to change in order to add the keywords.
Well I don't know Geany but I'll try to make what you wrote starting from the lang file, which should be the simplest thing to do
Stay tuned