This is a complex subject. I haven't figured out what to do myself. The question is whether there can be two jurisdictions, i.e. the US and Argentina. Can your will go through probate in the US if you died in Argentina as a permanent resident? My understanding is that the place in which you are living as a permanent resident at the time of death determines which jurisdiction has responsibility for all worldwide assets. If so, I can only imagine a huge mess should a permanent resident of Argentina die here with assets in both countries. Maybe there is a lawyer here who knows Argentine and US law. I'd assume that a will made in the US could go through probate if the courts there had no knowledge of assets in another country; likewise a will made in Argentina would apply to assets in Argentina, according to Argentine law, without special complications if the courts here had no knowledge of property elsewhere. CAN a person have two wills, each one for different countries? Or would assets in the US be subject to taxes and laws of Argentina?
Another consideration here is that inheritance laws are quite different from those of the US. Here you are obliged to give 80% of your estate to your spouse and children (50-50 of the 80%). You can not, under any circumstance, disinherit your spouse, children, grandchildren or even parents. If you have no linear direct relatives, you can will your entire estate to whatever or whomever you want. The only way that you can will 20% to someone outside your family is by stating it in a will (I should think notarized in Argentina to be safe and witnessed).
As for wills in the US, you can do it yourself but be careful. I know of a case in which ambiguous wording caused disasterous results.
If you get a clear answer on this, please let me know. Meanwhile. I really would look for a lwayer -- not just ANY lawyer but one who specializes in inheritance law.