After hpoussin fixed neutral string locales of *.inf files I'm updating —hopefully for the last time— the driver manifests, making all the Spanish strings neutral for all the sub-languages/variants.
Also, redo the awful (maybe even shameful) msgina translation, fleshing out the control positioning in the process and use the correct language code in comctl32, until now it wasn't even displayed and it did always fallback to English (so things like wizards and date pickers were always buggy). Fixing some slight typos and adding some contextual enhancements.
Overall I'm pretty happy with how nice everything turned out. I'd dare to say that it surpasses its Microsoft counterpart in clarity and terminology.