The resourcebundle.inspector project can inspect projects of unused properties keys or duplicate keys.
'de.alpharogroup:resourcebundle-inspector:2.2.0'
<dependency>
<groupId>de.alpharogroup</groupId>
<artifactId>resourcebundle-inspector</artifactId>
<version>2.2.0</version>
</dependency>
<dependency org="de.alpharogroup" name="resourcebundle-inspector" rev="2.2.0"/>
"de.alpharogroup", "resourcebundle-inspector", "2.2.0"