The hierarchy of precedence for different Language.properties files is:
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, Language-ext_en_US.properties has the highest precedence and the Language.properties file has the least precedence. The hierarchy is:
Language-ext_en_US.properties
Language_en_US.properties
Language-ext_en.properties
Language_en.properties
Language-ext.properties
Language.properties