A PatternLanguage is a concept invented by the US architect and philosopher ChristopherAlexander most accurately described in his 4-book series "The Nature of Order".
PatternLanguage is a method for understanding and changing living systems. It is a system analysis and a design methodology. The analysis part results in "patterns" which describe "solutions to problems in a context". The design part selects pattern and builds a generative process as a sequence of "applying patterns" in the form of "structure preserving transformations" to "unfold living structure".
All this is very much at the root of wiki (as a living and unfolding system) and can be supported by wiki if this is the goal of a community. But note that there are many other WikiApplications. Not each wiki is a PatternLanguageWiki.