I flew there about 4 years ago. As far a I can remember it would have been posible to get an Argentinian licence based on my FAA PPL, but my (lack of) language skills made that unnecessary. I understand that even if ATC understood your english, they would not be allowed to respond in english without an appropriate rating (probably a good thing) and only international airports had english rated ATC. You would have to have quite good aviation spainish to consider going alone, but even then a local instructor could give you some ideas about where to go, or more importantly, where not to go. I ended up hiring the aircraft with local instructors and paying their lunch and costs for a days touring. When I was there the currency had recently been devalued so everything seemed very cheep for me - the flip side to this is that genuine aircraft parts for maintenance would have been incredibly expensive for them! I remember how exciting it was seeing the one other GA aircraft flying while I was there (and yes I was looking!)
I think that it was about £50/hour dual in a PA28-235 and about £100/hour for a BE58 at the time. I will try to fish out some phone numbers and destinations if you're interested.