Feature request: Member preference for default language on multi-language site

As a addition to gettext support for static page content support to multiple languages (see #10), I would like to see option where Laddr member is able to select his/her language preference.

It would be also used when sending newsletter #43 or sending project updates on following/participating projects #4, so that Laddr can tell which language template, and which content language to send out.

It should be precondition before newsletter/updates automatic mailing implementation.