locale property
The browser locale to use for date and number formatting. The actual locale used for each chart is determined in three steps:
- If this 
lang.localeoption is specified, it is used. - Else, look for the closest ancestor HTML element with a 
langattribute, typically the<html>element. - If no 'lang' attribute is found, use the default browser locale.
 
Use en-GB, British English, for approximate consistency with
Highcharts v < 12.
Implementation
List<String>? locale;