That is tricky.. but do make a feature request for that.. the thing is infinitely scanning for a

Lang

folder was just not very performant, but maybe we can think of something a bit more pragmatic.. maybe

App_Plugins/SeoToolkit/Lang/Functionality.en-US.xml

and

SomethingElse.en-US.xml

- so we'd scan for any xml file in that directory and combine them.