I tried changing region to the system settings some time ago, then I set everything back. I noticed some things:
- Miiverse is in Japanese
- alle the games in the Friend List have Japanese titles
- the Save Data Transfer Tool is completely in Japanese
- some content inside the Mii Plaza is in Japanese
Not a problem for me but I wonder why setting those back to EUR and/or EN has no effect
I experienced this too. When you change System Setting's region then set it back, it kind of messes up. Change the console language manually and you should be fine?