Windows 10 Language Packs -

: Type the name of your desired language. Icons next to the name indicate available features, such as display language, text-to-speech, or handwriting recognition.

Set-WinUILanguageOverride -Language ja-JP windows 10 language packs

If you need to deploy language packs without internet (e.g., on an air-gapped PC), Microsoft provides and LXP (Local Experience Pack) .appx files via the Volume Licensing Service Center. You install them using DISM : : Type the name of your desired language