System locale is the language used when displaying text in programs that do not support Unicode. As for how to change it on Windows 10 computer, please read on.
Video guide on how to change system locale in Windows 10:
Step 1: Get into Control Panel.
Step 2: Tap Change date, time, or number formats to move on.
Step 3: As the Region dialog appears, choose Administrative and click Change system locale.
Step 4: Select a new system locale and tap OK.
Step 5: Hit Restart now to make the setting effective.