Now that you have an idea of locales, to take advantage of them in Grails you have to create message bundles that contain the different languages that you wish to render. Message bundles in Grails are located inside the grails-app/i18n directory and are simple Java properties files.

Each bundle starts with the name messages by convention and ends with the locale. Grails ships with a bunch of built in message bundles for a whole range of languages within the grails-app/i18n directory. For example:

messages.properties
messages_de.properties
messages_es.properties
etc.

By default Grails will look in messages.properties for messages, unless the user has specified a custom locale. You can create your own message bundle by simply creating a new properties file that ends with the locale you are interested. For example messages_en_GB.properties for British English.