Where to translate "1 of 5" on the forum?

Where to translate eg "1 of 5" on the forum?

Go to Admin->Settings->Language Settings.  In the manage keys block, type in _of and check the search box.  There will be alot of results but scroll down unto you see:

_of (System) Edit

This is the key you want to edit.

Unfortunately, I translated the key _of (System) a year ago and here it's not changing. Probably there is no key, just plain text "of", but I can't find the file.