The system's default paper size is initially set to match the preferred language in the International preference pane. US Letter is selected for English, and A4 is selected for other languages. You may change this in Print Center. Follow these steps:
1. Open Print Center (/Applications/Utilities/).
2. Choose Print Center > Preferences.
3. Choose a paper size from the Default Paper Size pop-up menu.
The default paper size will be used with any new documents you create. Existing documents will retain their previous paper size until you change and save them on an individual basis.
Note: A localized application may specify its own default size, but the system's default is used when an application is not localized for the selected language or region. This explains why applications may default to different paper sizes.
For additional information, users of the British keyboard layout should see technical document 106948, "
Mac OS X 10.2 (British): Paper Size Reverts to US Letter".