It's nothing to worry about - I've just used the code and as much of the last name as possible with AR on the end. So 'EB1234567 Smith AR' or 'SmithAR' with no space if there's not enough room. It's gone through every time. You definitely don't need the full name, I think the number and the country code is the most important thing.
Out of curiosity you're saying you've managed to send from a UK account to an Argentinian bank account directly? The app has always stoped me from being able to send directly to an account with an error or saying that the receiver 'requires a nationality', can you shed any light on it for me? Or did you encounter no other problems?
I just checked and it looks like they've updated to allow bank transfers from the UK so there's now an option on the android app for nationality etc. Just sent and will update when it's gone through, in case anyone else was having trouble sending from the UK!