To change the system default language, close your apps, and use these steps:

1. Open Settings.
2. Click on Time & Language.
3. Click on Language.
4. Under the "Preferred languages" section, click the Add a language button.

5. Search for the new language using the language or country name.
6. Select the package from the result.

7. Click the Next button.
8. Check the Install language pack option.
9. Check the Set as my Windows display language option.

10. Check the additional features as needed — for example, "Text-to-speech" and "Handwriting."
11. Click the Install button.
12. Click the Yes, sign out now button.
13. Sign back into the account.

After you complete the steps, the Windows 10 language will change across the experience, including the Sign-in screen, Settings app, File Explorer, Desktop, apps, browser, and websites you visit.