No question, just a post to share information to help others determine the language that the user has the application the application with.
In ExtendScript you could use
$.locale to get something back like “en_US” - at least in Adobe InCopy and Adobe InDesign
With UXP, if you have
const host_o = require('uxp').host;
then in Adobe InDesign
host_o.locale will provide the same “en_US”
But in Adobe Photoshop you need
host_o.uiLocale to get that same “en_US” value, or whatever language is installed.