Remove lang in path when standard

What do you mean by standard? I think an option to apply the language as a ?lang= in the query string also for clean urls would be better, then you could use apache .htaccess to either a) solve this problem http://drupal.org/node/190122 and b) solve your problem as well by having an option to assume a specific language if ?lang= is absent and using apache .htaccess to reintroduce it in front for "standard"-language.

There are interconnected issues here.

See http://drupal.org/node/208712