The support article Change your Apple ID country or region - Apple Support describes how to change your country setting on everything using your Apple ID, and the requirements and results of doing this.
Changing store country is not a trivial endeavor. The system is designed to only facilitate doing this if you are moving to the other country to take up residency. It makes it difficult for people to temporarily change country settings to do things such as get around distribution restrictions only allowing them to buy items available in the country where they live.
Because you have to cancel subscriptions you will lose access to the Swedish version of those apps. If you resubscribe with a Japanese country setting you will get the Japanese version, and you might have to pay for them if they cost money. Any apps you have on your phone now will stay there but you won't be able to update them unless they are Apple apps. The apps will work as long as the bank or whatever does not absolutely require you be using the latest version.
"Redownload your apps, music, movies, TV shows, and books on any devices that you might use to play or read them in the future. Some types of content might not be available in your new country or region. (Learn what types of content and services are available in your new country or region. - Availability of Apple Media Services - Apple Support )"
Any balance you have with Apple will have to be emptied.
No, this is not going to be a simple solution. The only other solution is to either try to find workarounds to having to use the Japanese apps (maybe web based services are available?), or to ask the ap distributors for a particular country to make their apps available in other countries.