I noticed there is a latex lexer in LexOthers.cxx, which is much better than LexTeX.cxx :)
However, this is still not perfect.
1. It has no folding function.
2. It colors everything with the same color in math environment. However, we know there can be comments and others in math environments.
I would like to share my modifications on the latex lexer. I've done a folding function that recognizes \part, \chapter, \section, ..., \subparagraph as well as \begin...\end, and also changed the behaviors of syntax coloring.
I'm now using this myself. Hope this is helpful for improving the lexer.
For non-developers who want to use it: Put the file in \lexers; delete the code about latex in LexOthers.cxx; add LexLaTeX.cxx to makefile; and rebuild.