From Xojo Documentation

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

Supported for all project types and targets.

The locale's separator for grouping a number. In "en-US", this is the 'comma' placed between every three integer digits.

Sample Code

Get the locale's grouping separator:

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

Var grouping As Text
grouping = locale.GroupingSeparator