Muchos gracias!

Fito: Creo que tu ingles es mejor que mi español. So I will use English. Do you know if voseo-using Hispanics understand tuteo?

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 ;).

I know why I prefer tú but why not use "usted" all the time? It seems a safe bet and there's no chance of being unintelligible or offending someone. For what it's worth, I would find voseo confusing (I can never remember how it's conjugated). Would Hispanics from tuteo societies be confused by voseo?

Well, there are also these localizers who find usted too formal, and there are companies who require localizers to use casual language so that their products seem more… “approachable” by consumers (Microsoft comes to my mind right now – they’ve required Windows Phone translators to use tuteo and simple language, at least in es_MX).

In a nutshell, there is no single solution for this whole mess that is Spanish. :P

As you guessed it, people unfamiliar with voseo may get confused. I don’t know how to conjugate it perfectly either, because it is not uniform across regions, let alone countries; and we use tuteo where I live.

To conclude, I think you can just use tuteo for a start and it’ll be okay. If the intended audience of the translated product finds it inappropriate (because, for example, they are all mature adults or seniors), it can be changed to usted.