NetBeans IDE 5.5, 6.0.1 is and soon 6.1 will be provided as multi-language and all possible localization files found in the installer will be installed by default. If a localization is available for your system locale, the IDE will show menus and UI messages in this locale.
If you want to use English US messages instead, you have two options:
1) You can force messages to show in English by switching your system locale to English. Example for Linux:
$ export LANG=C $ export LC_ALL=C $ ./netbeans
2) You can stay in your own locale, and start the IDE with the --locale parameter set to en. This works for the IDE and platform, but it may not apply to other applications, such as the Application Server (See: FaqStartupParameters). Example for Linux:
$ ./netbeans --locale en
Applies to: NetBeans 5.5, 6.0.1, 6.1 multilanguage releases
Platforms: All