There is a big problem with Telerik controls when using national resource files.  Switching from one language to another and again sometimes destroys the user interface. It especially concerns RadCheckBox control. Text, tooltip and probably other properties from one control appear in other control etc. I think it can be a general problem because I also noticed that sometimes Image from one RadButton control appears in other button.

I prepared a set of images which show how it happended in my case. Switching from Default language to Polish language and again and then adding and removing new RadCheckBox completly destroyed user interface in my sample UserControl. This new RadCheckbox was created as a copy of existing RadCheckBox what may be a clue.

I also attached VS2019 project with my sample UserControl.

Best regards,

Andrzej