Your keyboard types in the dominant language spoken in your country by default. If you want to write in a different language, whether it's to speak with a foreign friend or to fulfill an assignment in a foreign language class, follow these steps:
Step 1: Bring Up the Windows Menu
Step 2: Click the Settings Icon
Step 3: Open Time and Language
Step 4: Click Region & Language
Step 5: Click Add Language
Step 6: Select the Language You Want to Add
If you don't want to go through the list manually, you can use the search bar at the top of the list to go straight to it.