You can set your default language during the installation process of Red Hat Enterprise Linux 5 which also specifies your locale settings. To change the default language you do not need to restart or reinstall Red Hat Enterprise Linux. You can do this as root by running the language selection application. This can be accessed from the system menu by clicking System => Administration => Language or typing system-config-language from a terminal. This displays a list of supported languages from which you can select your preference. Clicking on the OK button sets the selected language as default. The figure below illustrates the language selection application.
You can also change the default language used on your desktop from the GDM language menu before logging in to your desktop.