The default behavior for the engine is to get the current language of the OS. If you’ve ever manually set a language though in the engine, editor, or ini file that setting will override the OS language.
If you open up your Region and Language settings in Windows you can change your “Format”. If that doesn’t work then you have a setting overriding your default locale.
You can also specify culture=jp on the cmdline or in the application using the console window.
What locale are you trying/expecting to get?