It depends on what you want to translate:
* Translating Wiki documentation (Trac* and Wiki*) is like editing
any other wiki pages
* Translating the error messages is quite easy, as they are in Python
files, but it is quite easy to locate them
* Translating the interface is far more tricky, as some elements are
defined in Clearsilver templates, so are hardcoded in the python files
in many (many) locations
* Finally, the most difficult piece is the report/query pages. I've
not been able to produce 100% translated results here
Trac 0.12 should provide support to ease translations
(internationalization/localization).
I would strongly recommend that you do not start any translation work
on Trac 0.10, as the templating engine has been changed for Trac 0.11,
which implies that all the template pages have been migrated to a new
format.
HTH,
Manu