Description
Special:NamespaceInfo (added in T263513) will describe namespaces added by extensions as just "Custom namespace <name>", unless a localisation message like "namespaceinfo-description-ns<id>" is defined for each namespace.
Extensions that add namespaces (with constant IDs – this won't work for configurable IDs) should define these messages. The message should describe the purpose of the namespace (it may contain links to documentation).
Examples:
- https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Wikistories/+/1080340
- https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Translate/+/1082128
Acceptance Criteria
- namespace descriptions added