How exactly can you use this names already?
Do you think it is useful to register such japanese domain names? What are the advantages or disadvantages?
ccTLDs are restricted only to their country of origin, based on agreements between
ICANN and the country in question. They can only be registered if you have an address
in that country, but the domain name extension can be viewed around the world.
This isn't true for quite a few ccTLDs. .ws is the most well known of these, but there are a number of other ccTLDs that anyone can buy.
Not many people have that plugin, and the SE's don't index it anyhow.
even CNN's spanish domain is "misspelled" - CNNenEspanol.com