Like Mac OS X, many applications are written to support more than one language, allowing all their user interfaces to display in the preferred language(s) along with Mac OS X. Since not all languages are supported by every application developer, the International pane in System Preferences lets you provide an order of preferred languages. Applications that don't support your first choice will display using the highest preferred language they do support.
While the diversity of language support is a must for Mac OS X and applications to be sold around the world, chances are that you speak only one or two languages. That means all those extra language files are taking up valuable space on your hard drive. You can trim down the footprint of Leopard and most individual applications (particularly apps with heavy language support like Microsoft Office or Apple's iLife, iWork and Pro apps) by removing unneeded localization files.
There are a couple of ways to go about this process. You can manually remove language files from applications by selecting an application in the Finder and using the Get Info command (from the File menu or the command-I keyboard shortcut). In the Get Info window, expanding the Language section will show you a list of language localization files bundled in the application. To remove any you won't need, select them and click the remove (minus sign) button beneath the list.
Note: The checkboxes in this list denote which languages you are choosing to enable; unchecking languages will prevent their use but not remove the localization files.
While manually removing localization files from individual applications is an option (and it's interesting to see which languages each application supports), it can be a time-consuming process. Another option is to use a tool such as Xslimmer (US$13; free trial), TinkerTool System (US$9.75; free trial) or Monolingual (free/donationware) to remove localization files from both Mac OS X and installed applications.
These tools make quick work of the process and also offer additional features that can be used with some of the other tips in this article. (Monolingual has not been updated to specifically support Leopard, though most users have not reported any problems using it with Leopard.)
2. Cut out the non-native code
When Apple made the transition from PowerPC to Intel processors in early 2006, it needed to provide solutions for two major problems. First, since Intel processors couldn't natively run code designed for PowerPC processors, Apple introduced Rosetta, a technology that allows an Intel Mac to emulate a PowerPC processor on the fly as needed to run PowerPC code. Rosetta makes all Intel Macs able to run software that has not been updated to run natively on an Intel processor.