I can see that many people will not like seeing posts from me written in Spanish (my native language)if they can't read it, but I also feel that some other people will prefer to have at least the interface in their language.
What I would propose is this: there should be a main language for every site and all the news written in that language should show up in the main page, independently of what language is chosen for the user interface. Additionally, any user could choose among the available languages to have news written in any of the show up in his/her main page too.
By the way, I will be migrating my test site to postnuke this weekend.