Just a little note, on my really busy days, as i recall, there were two options:
1. es as source lang, then translate en, then translate to a third lang (hard to keep up for fedora products)
2. es as source lang, then direct translation to a third lang (brazilliang lang was planned but no results so far)
I dunno about transifex limitations but i hope there will be no limitations on translators requirements. I do believe spanish <--> portuguese/brazillian is likely to happen translator case without English being the middle man (this translator might not handle english at all).