If you are running the latest Stable version of Luma.
1. Hold Select while booting Luma and make sure to enable Region Emulation.
2. Install
LumaLocaleSwitcher there is a QR code for quick installation with FBI.
3. Within the LumaLocaleSwitcher app click Titles and find Taiko, will come up as "TAIKO3" if using English Patch otherwise check your Japanese Titles.
4. Click "Change Region" and pick "JPN".
5. Click "Change Language" and pick "JP".
If you are running nightly/hourly/weekly builds you will need
this version of LumaLocaleSwitcher, steps are the same.
You could always do it manually, on SD card you would create a .txt file in "/luma/locales/" and call it "0004000000190E00.txt" inside the file would be "JPN JP", again the locale is different if using a newer version of Luma you would create a .txt file in ""/luma/titles/0004000000190E0/" and call it "locale.txt" with the same content as before "JPN JP"
Hope that helps, easier to just use the Locale Switcher