Heh. So, I decided to create a separate issue not to be confused with others.
ZBX-3300 (rev 16266) in file 'config.php' we see line# 887:
$confirmMesage = _s('Delete selected value mapping?');
but function "_s()" is not include the string to POT file !
It seems need to add it to the --keyword parameter.
I tested "--keyword=_s --keyword=_n:1,2" and it works !
Now in all locales (at end of PO files) we see obsolete messages marked by #~ header.
I prosed you to think about add use parameter '--no-obsolete' for additional command 'msgattrib' - Remove obsolete #~ messages.
Example: #msgattrib --no-obsolete --output-file=new_frontend.po frontend.po
Of course this is not problem, obsolete messages not presented in GUI editors like a Virtaal or Poedit and can be reused again if returned to source code, but i think it can be removed.
It's just a thought.
Note: Virtaal is much better that Poedit. IMHO.