It looks like some change in the software for Wikimedia recently caused four namespaces for LiquidThreads to become active in many (all?) Wikimedia wikis, even if LiquidThreads is not reported as installed on Special:Version for the wiki.

An issue was created by MZMcBride noting a breaking API change because "LiquidThreads API namespaces don't include canonical key"[1].

Werdna commented on IRC, as also included in the issue report, this is some "hugely annoying" "feature of the localisation cache".

Siebrand

[1] https://bugzilla.wikimedia.org/show_bug.cgi?id=24837