Hi Jan
Yes, re-installing Windows 10 would be the best option, that will ensure consistency of language across the operating system . . .
You can reinstall Windows 10 at any time, you do not need to worry about activation or a product key and it will not cost you anything !
Since you previously had Windows 10 installed and activated on that PC during the installation process skip the steps which ask for a product key and select the option 'I am Reinstalling Windows 10 on this PC', and activation will not be an issue, your PC will have a digital entitlement stored on the Microsoft Activation Servers
Make sure you install the same Edition of Windows 10 (Pro) you previously had installed to avoid Activation issues