language_default (in wikiconfig) sets the default language of a wiki's content.
The HTML lang attribute of a page's BODY tag is set to this language, except if you specify a different page content language in the page header like this:
#language he
The language name is the iso-639-1 name of the language. Languages that moin does not support are ignored.
This is critical if the wiki contains content in different directions, like Hebrew pages, which should display in right to left direction, and English pages, which should display in left to right direction.
In the past, system pages had a language comment: ##language:en. This comment has no effect, and should be changed to the new #language en format. To repair old pages in your wiki, run scripts.repair_language.py in your wiki data directory. Back up your wiki data directory before doing this!