Change I58a9cdfe60c7b9027bf031c91370472054f04ae2 made MediaWiki rely on CLDR data for plural rules (see languages/data/plurals.xml). CLDR apparently lists Vietnamese as having no plurals. While it’s true that Vietnamese doesn’t inflect for plurals, the language does absolutely have the concept of plural number. Plurals are typically marked by “các” or “những” in front of the noun.

MediaWiki’s Vietnamese localization uses the plural: magic word extensively, just as the English localization does, to add these markers in the “many” case or omit the number 1 in the “one” case. These usages are now broken throughout the interface. The rules for Vietnamese should be overwritten in plurals-mediawiki.xml to be identical to that of English:

<pluralRule count="one">n is 1</pluralRule>

Please note this requirement when implementing the JavaScript plural parser.

Version: 1.20.x
Severity: major
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=40251