If your question is about creating a web app, exposed in Genesys Desktop, using a Custom Client Application integration or an Interaction Widget integration (see here) or a Premium Application Wizard/Installer, it is possible to get the environment/region as url parameter.
Genesys Desktop supports url interpolation with these 3 type of integrations. When the Genesys Desktop loads the web app (as Custom Client App, as Interaction Widget or as Premium Application), it will invoke the url defined in the integration and it can pass region and language of the user who is making the call to the web app from his Genesys Desktop.
Note that there is an error on this page. The url configured in the integration (Custom Client App, Interaction Widget, Premium App) should be: https://myapp.com?langTag={{pcLangTag}}&environment={{pcEnvironment}}
When Genesys Desktop loads the web app, it will invoke the configured url replacing {{pcLangTag}} and {{pcEnvironment}} with the language and Genesys Cloud region of the logged in user: https://myapp.com?langTag=en-us&environment=mypurecloud.com