From Xojo Documentation

Read-Only Property (As Text )
TextValue = aXojo.Core.Locale.Identifier

Supported for all project types and targets.

This is the locale's identifier. The identifier may not exactly match the identifier passed in via the constructor due to conversions (e.g. 'en_US' could become 'en-US').

Sample Code

Get the locale's identifier:

Var locale As New Xojo.Core.Locale("en-US")

Var id As Text
id = locale.Identifier