Suddenly my Calculator name got changed to something chinese and I don't know how to revert it..!
Try to uninstall the calculator app and reinstall it from Windows store. Or you can manually uninstall calculator a PowerShell command::
Get-AppxPackage *windowscalculator* | Remove-AppxPackage
You can get more here::
You can also use CCleaner to uninstall the calculator app.
My guess is that your computer is infected by a badly-written Chinese virus that replaced your calculator program.
I would suggest to scan your computer deeply with several anti-virus products, including first Windows Defender and Malwarebytes Free. You may also follow with some online anti-virus scans that do not need installation. See the article Test comparison - Which is the best free online antivirus scanner?.
Then follow with sfc /scannow to check system integrity.
If the calculator does not change back, delete the program and copy it from another computer. The best solution in that case is to do a clean re-install of Windows, but that might not be convenient.
Just found this help thread through Google, I was just experiencing the same problem. I went to settings - applications - calculator - advanced options, then reset the app. It went back to English and is fine now.