In principle, the answer is yes, but the ICANN establishes certain limits or exceptions (countries officially recognised by the UN, other regions, and some others). The PuntuEus Foundation will be reserving certain names that are special for the community of the Basque language and Basque culture without having a clear owner, for example euskara.eus, euskalherria.eus, kultura.eus, etc. So if the domain you want to register is on the list of exceptions, you won’t be able to register it. Even though until now domain names of less than 3 letters have been reserved, the ICANN has opened up the means for registering 2-letter ones so they too will soon be available.
Accents, diaereses and «ñ» will also be allowed in domain names (they are also accepted by the browsers) and the person who registers ñabardura.eus will also register, automatically and free of charge, nabardura.eus too, and both of them will function as if they were a single domain.