I cannot change my keyboard layout to Japanese.

Try these Windows 11 checks in order:

1. Verify Japanese is still installed
   • Go to Start > Settings > Time & language > Language & region.
   • In the Language section, confirm Japanese is listed.
2. Switch the keyboard layout from the taskbar
   • In the system tray, select the input language icon.
   • Choose the Japanese keyboard layout from the pop-up list.
   • A faster shortcut is Windows key + Spacebar to cycle through installed keyboard layouts.
   • If Windows key + Spacebar does nothing for Japanese, only one relevant keyboard layout may be available for that language selection.
3. Check whether the Japanese keyboard layout is attached to the language
   • In Settings > Time & language > Language & region, select the ellipses next to the language that contains the keyboard, then select Language options.
   • Under Keyboards, verify the Japanese keyboard is present.
   • Keyboard layouts are not always stored under the matching language, so also check the current Windows display language entry if needed.
4. If an unwanted or stuck layout is interfering, remove and re-add it
   • In Settings > Time & language > Language & region, open Language options for the language that contains the keyboard.
   • Under Keyboards, select the ellipses next to the keyboard and choose Remove.
   • If Remove is greyed out, that keyboard is the only installed layout for the current Windows display language, so another keyboard layout must be added before it can be removed.
5. If extra or incorrect layouts return after restart, sync the administrative language settings
   • Open Control Panel > Region > Administrative.
   • Select Change system locale and set it to the same language as the system location/language.
   • Then go to Settings > Time & language > Language & region and open Administrative language settings.
   • On the Administrative tab, select Copy settings.
   • Enable Welcome screen and system accounts and New user accounts.
   • Save, then restart the PC.

Important:

• Changing the keyboard layout only changes the layout. It does not change the Windows display language.
• If Japanese cannot be added as a display language and messages such as Only one language pack allowed or Your Windows license supports only one display language appear, Windows may be using a single-language edition.

References:

• Manage the language and keyboard/input layout settings in Windows
• Problems in my Windows 11 keyboard - Microsoft Q&A Laptop model: Lenovo Thinkbook ITL 15 Gen 2
• Windows changes keyboard language settings - Microsoft Q&A
• I can't remove redundant keyboard layouts - Microsoft Q&A