[wp-trac] [WordPress Trac] #55412: Language "German (Austria)" outputs html lang incorrectly as "de-DE" not "de-AT" since WordPress version 5.9

[WordPress Trac]

#55412: Language "German (Austria)" outputs html lang incorrectly as "de-DE" not
"de-AT" since WordPress version 5.9
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 Reporter:  simjost       |      Owner:  (none)
     Type:  defect (bug)  |     Status:  new
 Priority:  normal        |  Milestone:  Awaiting Review
Component:  I18N          |    Version:  5.9
 Severity:  major         |   Keywords:
  Focuses:                |
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 Since version 5.9 including 5.9.1 and 5.9.2 the lang attribute in the html
 tag for the language/translation "German (Austria)" is incorrectly output
 as "de-DE". This would be correct for plain German, but for the region of
 Austria it should be "de-AT".

 Downgrading to 5.8.4 fixes the issue.
 Other languages/translations like "German (Swiss)" and "English (UK)" and
 "English (US)" don't have the same issue.

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Ticket URL: <https://core.trac.wordpress.org/ticket/55412>
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