Automatic detection of user's preferred language

Here's what I did, it's quick, dirty and working(?):

Invalid language.

You need to specify a language like this: <source lang="html">...</source>

Supported languages for syntax highlighting:

actionscript, ada, apache, applescript, asm, asp, autoit, bash, blitzbasic, bnf, c, c_mac, caddcl, cadlisp, cfdg, cfm, cpp, cpp-qt, csharp, css, d, delphi, diff, div, dos, eiffel, fortran, freebasic, gml, groovy, html4strict, idl, ini, inno, io, java, java5, javascript, latex, lisp, lua, matlab, mirc, mpasm, mysql, nsis, objc, ocaml, ocaml-brief, oobas, oracle8, pascal, perl, php, php-brief, plsql, python, qbasic, reg, robots, ruby, sas, scheme, sdlbasic, smalltalk, smarty, sql, tcl, text, thinbasic, tsql, vb, vbnet, vhdl, visualfoxpro, winbatch, xml, z80

I have three directorys in /sites/mypage/ where I redirect to.