The PHP escapeshellarg function depends on your current locale. I think it’s bad, but PHP developers made this choice. If like me your default locale is ‘C’ you lose all UTF8 characters.
They suggest you to call something like setlocale(LC_CTYPE, "en_US.UTF-8"). It doesn’t work if the en_US.utf8 locale is not installed on your system. Of course maybe you have the fr_FR.utf8, or de_DE.utf8, but you will have to try all of them until you find one utf8 matching locale. And if there is not, you’re screwed. It’s also bad if you want code that runs everywhere.
Simply use that:
$escapedArg = "'".str_replace("'", "'\\''", $arg)."'";
It will do the same as the escapeshellarg function: replace yourstringthat'slong by
'yourstringthat'\''slong'
as described in the escapeshellarg manual (and I also looked into the PHP source code to be sure).
See also: