These are the languages known by GeSHi that can be used in the lang parameter.
abap
actionscript
ada
apache
applescript
asm
asp
autoit
bash
basic4gl
bf
blitzbasic
bnf
c
c_mac
caddcl
cadlisp
cfdg
cfm
cil
cobol
cpp-qt
cpp
csharp
css
d
delphi
diff
div
dos
dot
eiffel
fortran
freebasic
genero
gettext
glsl
gml
gnuplot
groovy
haskell
hq9plus
html4strict
idl
ini
inno
intercal
io
java
java5
javascript
kixtart
klonec
klonecpp
latex
lisp
lolcode
lotusscript
lua
m68k
make
matlab
mirc
mxml
mpasm
mysql
nsis
objc
ocaml-brief
ocaml
oobas
oracle8
oracle11
pascal
per
perl
php-brief
php
pixelbender
plsql
povray
powershell
progress
prolog
providex
python
qbasic
rails
reg
robots
ruby
sas
scala
scheme
scilab
sdlbasic
smalltalk
smarty
sql
tcl
teraterm
text
thinbasic
tsql
typoscript
vb
vbnet
verilog
vhdl
vim
visualfoxpro
visualprolog
whitespace
winbatch
xml
xorg_conf
xpp
z80