I am unable to find an example illustrating the appropriate content that should be included within this file to localize the function category name
Discussion posts and replies are publicly visible
It depends on the structure of the function you are implementing...
In appian-plugin.xml the following lines must be added.
<appian-plugin name="<FunctionsProjectName>" key="<package>">
<plugin-info>
<description>Description</description>
<vendor name="xxxxxxx" url="https://www.xxxxxxx.com" />
<version>1.0.0</version>
<application-version min="16.2" />
</plugin-info>
<function key="<functionKey>" class="<mainClassWithPackage>"/>
</appian-plugin>
And in properties file (<functionKey>_en_US.properties for example.),
function.<functionKey>.description=Description
function.<functionKey>.param.<paramName>.description=PArameter Description