How do I filter for stations in a specific country?
 

For example, I want to see the list of stations in japan.

What about UK and other countries?

How do I do that?

you cannot as the means to query such details has not been enabled (although it has been coded as part of the v2 platform) as not enough of the stations listed provide it for the location to applicable (even after someone spent 3 months trying to populate that information).

How do radio apps sort stations by country?
 

Do they do it by hand?

you can find a directory that has that option to filter by location

and this just reiterates the key issue when it comes to broadcasters, they don't want to update the software due to downtime and loosing historically inaccurate peak listener numbers and other 'uptime' values when it's actually something the listeners want as the features being requested are the things that have been implemented but cannot be effectively used as it needs the broadcasters to update. so now we're in a chicken and egg scenario and it's primarily the listeners who loose out.