In Umbraco we have some wierd conventions for language files, as in they can actually be placed in 3 different folders and still work just fine.
The placements are:
- /App_Plugins/Test/lang/en-us.xml
- /config/lang/en-us.user.xml
- /wwwroot/app_plugins/text/lang/en-us.xml
Here is Kevin Jumps PR where he mentions all 3: umbraco/Umbraco-CMS#12206