TextMate is smart enough to not underline your keywords and commands, so just use the system spell checker if your language is supported.
What am I doing wrong ? While some keywords are well recognized (\label, \begin, \date), others are certainly not. I find many LaTeX commands such as \noindent, \rightarrow, \maketitle, \renewcommand ... that are underlined. Do I have to teach them ? and how ?
Regards
Christof