Modules and go mod

This program prints an order total with thousands separators, using a package from outside the standard library. The code is correct, and it does not build.

// file: main.go
package main

import (
	"golang.org/x/text/language"
	"golang.org/x/text/message"
)

func main() {
	var total int64 = 1234567
	p := message.NewPrinter(language.English)
	p.Printf("Order 1001 total: %d cents\n", total)
}
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main.go:6:2: no required module provides package golang.org/x/text/language; to add it:
	go get golang.org/x/text/language
main.go:7:2: no required module provides package golang
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