Thread:User talk:Fitoschido/Muchos gracias!/reply (3)

I would say they all understand tuteo, although they may find it awkward to use in casual speech. A safe bet is to use formal Spanish for any locale (i.e., using usted). In fact, this is historically the standard treatment in software localization into Spanish, but MediaWiki (and web sites such as Facebook, Twitter and Google apps) deviate the norm ;).