Manual Cache : filenames with specific letters not visible

If i use for area-filenames specific german letters like u with the two dots above, then i have no visible filename after downloading the area.
I cannot mark this file with the checkbox without a visible name. I cannot delete the file. I cannot continue a paused download either.
Maybe the problem also occurs with other country-specific characters in filename ?

My question:
Does the flight simulator work with a file without a visible filename, or is this area-download
ignored ?
is there a possibility to delete the file or to give it a different name?
( no highlighted option for this.)

unfortunately I cannot see how much space is still free in the local-cache file.
that would be desirable.