Thread:Project:Support desk/MediaWiki v1.19.1 installation: Compilation failed: support for \P, \p, and \X has not been compiled/reply (3)

\P is a unicode regex. The installer should check for unicode support and fail if it is not available. (and i believe that check was there in 1.16 too). If you can install mediawiki without Unicode PCRE support, it is a bug.