Language/display information is defined in Language.properties, as well as various other Language_<LanguageCode>.properties files for foreign languages. These files are obtained on extracting the portal-impl.jar file, and are placed in the content folder. Language.properties is the primary and "default" language definition file, but definitions in that file may be overridden by language specific definitions. For example, the file Language_en.properties contains the English versions of most of the definitions. The file Language_fr.properties contains the French version, etc.
Language files can further have locale specific definitions. The Language_en_US.properties file (if it exists), contains the English phrase variations further defined for the United States. Other languages can also have locale specific definitions.
The following is the hierarchy of precedence for different Language.properties files to override each other:
Language-ext.properties takes precedence over Language.properties.
Language specific versions take precedence over the non language specific versions. For example, Language_en.properties takes precedence over Language.properties.
Location specific versions take precedence over the non location specific versions. For example, Language_en_US.properties takes precedence over Language_en.properties.
For the Language.properties file for English, the following is the hierarchy of precedence, where Language-ext_en_US.properties will have the highest precedence and the Language.properties file will have the least precedence:
Language-ext_en_US.properties
Language_en_US.properties
Language-ext_en.properties
Language_en.properties
Language-ext.properties
Language.properties