CTRL+R also is the de facto Windows standard for Reload/Refresh.
I doubt that.
In MS Word and MS powerpoint Ctrl-R puts [...]
You completely misunderstood the meaning of that sentence. It means that Reload/Refresh is almost always carried out by CTRL+R. It does not mean, that CTRL+R always carries out Reload/Refresh. There is a major difference.
Snow is always cold. But not everything which is cold is snow.
Your posting is confused and seriously at war with logic. I actually added your examples (Word, Powerpoint, etc.) to my list above, because they are in favour of my arguments, not yours, since none of them use CTRL+R to delete anything. Instead, they further add to the list of "programs which use CTRL+R for vital operations" (as already said in my previous posting) and to which MP3Tag users may realistically be expected to be used and accustomed.
Assigning a general purpose letter such as "R" for deleting is just as arbitrary and error-prone as any other letter, i.e. "D" for Delete. Or "E" for Erase. Haven't checked, but I'm sure that CTRL+D and CTRL+E are also used by lots of programs for standard operations. Hence why you have a key specially dedicated to this task: the del key ("entf"). (And to a minor degree also the backspace key).
Together with the modifier keys (CTRL, ALT, SHIFT) there are endless possibilities of combinations for the del key, so there really is no need to use any letter key for deleting operations! That's just bad practice and unsafe program design.
Not to mention that it's easy to accidentally press CTRL+R, when you were in fact reaching for a key in proximity (not all of us use the "eagle method"...). If at all, this happens only much harder with the del key which is more dislodged from other keys on every keyboard layout that I know.
Not even counting the rest of the list, the mere fact that Microsoft Internet Explorer AND Microsoft Windows Explorer use CTRL+R for Reload/Refresh makes it a Windows standard.
And you said yourself, that "Apple based programs use Ctrl-R to reload". So given that put together this covers 98% of all operating systems worldwide, your point must be that it's "not really a standard" on Free-BSD and Sun Solaris ... well I give you that.
Thinking of it, I can't even give you that, as MP3Tag doesn't even run on these systems.