Resource bundles are usually stored in property files. However, as property files are plain files, issues with the encoding of the file may arise. The XML resource bundle format has been developed to provide an alternative to property files.
The XML format declares the encoding of the file. This avoids use of the native2ascii program which can interfere with encoding.
Property files generally use the ISO 8859-1 character encoding which does not cover the full unicode charset. As a result, languages, such as Arabic, would not be natively supported.
Tooling for XML files is better supported than the tooling for Java property files; thus, the XML editor copes well with the file encoding.