Resource bundle is a set of properties files that have same base name with
different language-specific suffixes.
A resource bundle contains at least two properties files with similar base name, for example file_en.properties and
file_de.properties.
IntelliJ IDEA recognizes properties files, and if two or more properties files with the names that differ only in suffix, are encountered, joins them into a resource bundle. The new node Resource Bundle '(base name)' appears in the Project Tool Window:

IntelliJ IDEA supports the following features for the resource bundles:
- Dedicated Resource Bundle Editor
- Error highlighting for the missing properties or values.
- Refactoring for resource bundles includes Rename, Move, Copy and Safe Delete.