If you buy a brand new PC, you'll be prompted during initial set-up to choose your default language.
Whether you accidentally chose the wrong language, simply want to change it to a different one, or your machine was already configured for you, it's possible to change your language on Windows 10 at any time.
It should be noted that changing the default language in Windows 10 will mean the newly selected language will be everywhere on your computer, in its own settings and on the internet.
Here's how to do it.
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How to change your language on Windows 10
1. Click on the Windows start menu and type "Settings," selecting the top option that appears in the search result.
2. In the Settings app, click on "Time & Language," then click on "Language."
3. Under "Preferred Languages," click on "Add a preferred language" and begin typing the name of the language you wish to use on your computer.
4. Once you've found your preferred language, click "Next" to install the language pack on your computer.
5. On the "Install language features" screen, make sure to check the "Set as my display language" option just under the selected language. Check the "Install language pack" option as well.
6. Click "Install" when finished and the pack will begin to download.
7. When finished, you will be prompted to sign out of your Windows 10 account. Do so, then sign back in to see your new language displayed.