We are part of the "Americas" ladder but we have a different server cluster for SA.
As for language it all depends on where the people in the team are from, if u have brazilians, argentinians and chileans on the same team it'll be either "portuñol" (similar to what u guys call spanglish, works well for basic calls but beyond that people will get confused) or english.
We don't have as many players as you guys do so our high level ladder matches will always have diamonds to gm (sometimes even plats and golds get in) mixed in a big pool which makes most matches a terrible enviroment for getting better at the game. Some players will take the VPN/Firewall route to play NA with high ping (~170ms) to circumvent that.
My london no bueno desculpa for the mistakes o_O
edit: I might be wrong but i think Peru, Bolivia, Equador, Venezuela, etc have their own server cluster aswell (or they go to NA since their ping to USE isnt that high). I don't recall ever queuing into any players of those countries in sae1.