To completely delete a file/folder from a project, the user has to change the Language view to the source language and delete the specific file/folder there. Then, for further operation, the view must be changed back to the target language again.
Although I'm an old user Trados Studio, I still cannot comprehend why this simple act (deleting a file/folder from a project) is so complicated. Adding a file/folder to a project had been similarly complicated before. Finally, the command Quick Add Files was introduced (as an enormous development).
I would warmly welcome a "Quick Delete Files/Folders" function, or even the removal of the multilingual language system of file management.