Here is the text of the announcement:
MazaCoin Press Release: First Sovereign National Crypto-Currency In History Announced
Friday - December 27, 2013 12:00 Noon ET USA
The MazaCoin Development Team is proud and honored to have been commissioned by the Oglala Lakota Nation to create for them the first ever Sovereign National Crypto-Currency. It is rare in history when we witness any nation creating a new sovereign coinage. This alone makes this an historic moment. The Oglala Lakota Nation have internationally recognized sovereignty, and their right to mint currency is guaranteed by treaty. And in fact the Oglala Lakota Nation has already exercised that right symbolically by minting collectible coinage and trading rounds.
Choosing to deploy a genuine and functional national currency is nevertheless a bold initiative. Choosing to utilize a Crypto-Coin for this purpose is truly innovative and courageous. It will change the lives of the Oglala Lakota people forever.
All the information you need is available on the MazaCoin website. We encourage everyone to follow the MazaCoin Twitter account for real-time updates on the MazaCoin launch. The MazaCoin Development Team is available to answer any of your questions about the coin's deployment. The MazaCoin Development Team does not speak for the Oglala Lakota Nation, it's government or it's people. Our focus is to give them the best Crypto-Currency possible as part of their National Heritage. We are volunteer Crypto-Currency programmers, miners and enthusiasts.
MazaCoin is but one part of the BTC Oyate Project directed and founded by Payu Harris. The BTC Oyate Project has as it's goal the introduction of Crypto-Currency into the Oglala Lakota Tribal economy. MazaCoin is one aspect of this plan. A Crypto-Currency exchange haven and mining farms on Tribal lands is another. Any questions regarding the socio-economic impact of MazaCoin on the Tribal economy, or other aspects of the BTC Oyate Project - should be directed to Payu Harris.
SINCERELY -- The MazaCoin Development Team
I bolded the key statements. So by treaty with the U.S. government, the Oglala Nation has the right to mint new currency. Not only is this right recognized by the U.S., but also apparently internationally.
So to answer the original OP question, MZC is the only cryptpo-coin that in UNAMBIGIOUSLY LEGAL INTERNATIONALLY.
Furthermore, similar to Casinos, apparently they may have also the right to run a legal exchange!