First of all, check if there is a Qt translation for your language. Qt Creator will only load translations if both are present.

Note that an untranslated ts file is currently not provided.

Translating Qt Creator requires using the linguist tools from the upcoming Qt 4.6 (master branch). You need to checkout and compile Qt master
(as described in the Qt translation process)

[assuming Linux]

1. Using git, obtain a checkout of Qt Creator from http://qt.gitorious.org/qt-creator
   
2. Add your language to the language variable of share/qtcreator/translations/translations.pro
   
3. With Qt (master) set up , run qmake and make in the Qt Creator directory.
   
4. Change to the share/qtcreator/translations and run
   make ts
   
5. Translate the ts file using linguist.
   
6. Run
   make
   to generate the qm files.
   
7. Set the LANG environment variable to your language and verify the
   results by running Qt Creator
   
8. Revert the ts files of the other languages
   
9. To update Qt Creator, do (in the Qt Creator directory)
   
   • make distclean
     
   • ‘git pull’
     
   • Continue with step 4,
     
10. Before a release, submit the change to your branch and ask for it to be
    integrated
    (http://qt.nokia.com/developer/the-qt-contribution-model)

Points to consider:

• Do not translate the Legalese (About dialogs).