The mod will be developed and localized in English. Before every major update pack (not the minors), I, as I am from Germany, will translate the mod into German as well (not really a lot of translating work, but a lot of writing texts, so it is quite a lot of work hindering quick development on the fly).
I really want the classic Hearts of Iron languages French and Spanish also to sport their own versions as well, but my French is poor and my Spanish non-existant, so a supporting translator (please only mother-tongue) would be needed.
Languages like Russian, Chinese and Arabic would be appreciated as well if you want to do the work, but I really aim for English-German, then for French-Spanish support. The non-English versions would only be updated after major content patches.