Windows 10 Pro - Serbian Latin keeps returning

Hello all,

I started the new thread as https://community.spiceworks.com/topic/1871102-windows-10-us-language-repeatedly-returns?page=1#entr... was solved. 

I am a freelance translator so I have installed these keyboards on my notebook: Czech, English (UK), Italian (Italy), French (France), German (Germany) and I recently also installed Serbian (in Latin) on my notebook (in the Czech Republic) but did not notice a box for the "main language" (did not remember anymore) was ticked. 

I tried to uninstall it easily with the control panel, but under Hours and Regions, there is NO Language bar (simply missing). I tried to add it, but it seemed to be too complicated.

Then I tried to simply uninstall the Serbian in Latin with the command  lpksetup.exe /u sr-Latn-RS but even when I did the Serbian text reappears anywhere (in some applications etc.), so I repeat the uninstall... then it recovers again.

When looking into the registry I found that apart from a Language folder, there is also a Language Groups folder: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Nls\Language Groups

BTW, should there normally be a Language Groups folder?

Then I realized there are about 3-4 lpksetup.exe.mui files not in the C:/Windows/System32/ apart from the lpksetup.exe file correctly placed at C:/Windows/System32/ 

So I installed the latest AdwCleaner 7.2.3 but lpksetup.exe.mui files are stil there.

Another thing you should know is this one: under the Start-Settings-Region and Language there is under "Language": Display Language of Windows: only Czech and underneath there is Preferred languages there is Serbian.

Could you please help me to find a solution as I have seen so many pages in order to find a solution but without any success.

Thank you very much in advance for your feedbacks.

Milada