There is two ways of buying games on other eShop regions
Create a Nintendo account for each
country / region you want to buy a game in. You will need a different email address for each
of those accounts.
Protip: if you have a Gmail account, put anything behind a "+" just before the @
and it will still points towards your email. Ex: [email protected] is the same
as [email protected]
Change your account country / region
each time you want to buy in a different eShop region. You will need to empty any credits in a
country before leaving it, or you will lose them.