When localizing an application (see JavaScript property files for details on localizing JavaScript), you will need to create new properties files for each locale. The files for the default locale are named simply as SomeFile.properties. The files for other locales are identified by appending the locale identifier to the end of the file name after a separating "_" (underscore) character (i.e., between the name of the page and the .properties extension). For example, SomeFile_es.properties would be the name of the Spanish language version of SomeFile.properties.
It is useful to note that if a particular property is not found by the application in SomeFile_es.properties, the properties file for the default locale, i.e. SomeFile.properties, will be searched. This is particularly handy in the case of Image.properties, described below, where only some of your images contain text and thus need to be localized. Properties for the other images can be defined once in the default locale properties file and they will be picked up in all locales.
Once done adding localized .properties files, update the LOCALE_LIST environment variable as appropriate (this variable defines the list of locales the client will be built for), for example, set it to "en,es" for a default English language application and a Spanish language application. See Application Locales for more details on this setting.
The merging of localized properties files from different components happens in exactly the same way as it does for default locale properties files. See Externalized Strings for more details on the merging of properties files.