The idea of Pattern languages was introduced into architecture by Christopher_Alexander? in the 1970s. The idea was picked up by programmers in the 1980s (see WikiWikiWeb?). Now some we are are trying to introduce it into GameDesign.
In its simplest form, a pattern language is just the collection of all patterns relevant to the task at hand. It is possible to put more structure on top of this - Alexander for instance organized his patterns generally from larger (distribution of cities in an region) to smaller (how to build a wall.) In addition, each pattern lists the larger patterns that it refines, and the smaller patterns that one should turn to for further refinement.
Some of Alexander's recent work has focused on GenerativeSequences, smaller, very specific subsets of the language presented in an order appropriate for a particular task.
Developing a formal grammar is outside of the current practice in pattern theory, and also not in the original mission of the wiki. But it might make for an interesting parallel development.