Set default dictionary according to locale in the browser
Originally created by Tails on #5962 (Redmine)
The fix for fix default iceweasel spelling language (#5371 (closed)) (using the amnesia branding extension so that it sets the preferred dictionary according to the current locale) does not really work that well. For most languages we testing on 0.17~rc1, no dictionary was selected by default. English had one, though.