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According to the documentation (and 6.0 and 5.2), you specify the language with something like "lang en". However, on 6.1 this produces a python exception because it can't find the abbreviation "en". Looking at todo.py, you need to specify "en_US" instead. It is a shame that "en" is not a valid abbreviation any longer. The documentation is wrong. It appears to me that the 6.1 documentation is documenting the 6.0 kickstart file format.
Changing the component to "install-guide"
The 6.1 kickstart documentation was extrememly lacking on several points. I will have this added as documentation errata on the website. Red Hat Linux 6.2 kickstart documentation has been vastly improved and this is now correct in the 6.2 kickstart appendix of the Reference Guide.