Get the first day of the week for a given region.
package main
import (
"github.com/noamt/go-cldr/supplemental"
"golang.org/x/text/language"
)
func main() {
tag, _ := language.Parse("en-US")
region, _ := tag.Region()
weekDay := supplemental.FirstDay.ByRegion(region)
println("First day is", weekDay)
}