Hi Jason!
Alex has a good point there, spanish anchor text inside english text will just look spammy.
One thing to remember is that Google recognize synonyms and other languages as well. If you want to build links for the spanish word "perder peso" and find it very tough to make it effective, links from english sites with the english anchor text "weight loss" will help you as well (the effect might not be as good as with spanish, but it will help).
Google will understand that "perder peso" equals "weight loss". But the recommendation is to work with links for the goal language, it´s most relevant for the users and in the eyes of Google.
