Isn't there some way to use standard wikitext to achieve the same rendered result as
$ GET http://abj.jidanni.org/index.php?title=MediaWiki:Sidebar&action=raw * navigation ** mainpage|mainpage-description ** Special:NewPages|newpages ** Special:Categories|categories ** recentchanges-url|recentchanges ** randompage-url|randompage * SEARCH * TOOLBOX * LANGUAGES
That way there would be no need to maintain a separate "sidebar language" interpreter.