Creating a sub-wikis should use the main wiki language settings

When you work with a wiki farm you expect all sub-wikis to work with the same default language as the main wiki (90% cases).
As an example i'm on a french main wiki which create english sub-wikis.
It's generating a task for the admin and a possible issue for non english speaker using XWiki.

I propose that the language settings in sub-wikis are, on creation, copied from the main wiki.