Strange PHP UTF-8 Behaviour
Shouldn't it be
$text = preg_replace('#[^\pL\d]+#u', '-', $text);in line 6. If you escape the \ you'll have a literal \ in your exclusion class. So the regex [^\\pL\d]+ finds one or more occurrences of a character not being a \, p, L or a digit. This would explain why "Développeur Web" will be reduced to "-pp-" - everything up to the first p matches and will be replaced by a -; the same is true for everything after the second p.
Perhaps there is a difference between both machines in how an escaped \ is treated.
EDIT after OP comment:
Actually escaping the \ is no problem here - both versions are treated the same way. What actually seems to be the problem ist, that the used PCRE version does not support unicode properties and wasn't compiled with --enable-unicode-properties.