b228a0aa44
Backport #15452 Fix #14793. The previous implementation used the first return value of matcher.Match, which is the chosen language tag but may contain extensions such as de-DE-u-rg-chzzzz. As mentioned in the documentation of language package, matcher.Match also returns the index of the supported tags, so I think it is better to use it rather than manipulate the returned language tag. Co-authored-by: Naohisa Murakami <tiqwab.ch90@gmail.com>