Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go1.11 linux/amd64

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

linux/amd64

What did you do?

I tried to use message.MatchLanguage("nl") to obtain language.Dutch, as per the example on its site.

See the following code for an example:

package main

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

func main() {
	nl := message.MatchLanguage("nl")
	fmt.Println(nl) // Prints "und", expected "nl"
	fmt.Println(language.Dutch) // Prints "nl" as expected
	p := message.NewPrinter(message.MatchLanguage("nl"))
	p.Printf("%.2f\n", 5000.00) // Prints "5,000.00", expected "5.000,00"

	p2 := message.NewPrinter(message.MatchLanguage("bn"))
	p2.Println(123456.78) // Prints "5,000.00", expected "১,২৩,৪৫৬.৭৮"
}

What did you expect to see?

I expected to receive language.Dutch, so that when I called p.Printf("%.2f\n", 5000.00), I would get "5.000,00", as Dutch uses "." for thousand separators and "," for decimal separators.

What did you see instead?

Instead message.MatchLanguage("nl") returned the und Tag rather than the Dutch Tag. And therefore when I called p.Printf() as per the example on the package's description, I got "5,000.00", which ironically matches the example in the description, but the example is wrong.

I also tried the third example in opening example, which also did not seem to produce the expected result.

It seems to me that message.MatchLanguage() either does not work or does not work as described.

Note: Making a new Printer with language.Dutch works as expected.