How to change language?

The bureau tab is really there to show you what's possible. It's not the best default and it's not very attractively done. Everything on the bureau page is available in blocks which gives you some flexibility where to put it.
You can't edit the menu tabs, like on the user page without using hook_menu_alter, in MYMODULE.
to delete the tab, do this

function MYMODULE_menu_alter($items) {
  unset($items['user/%user/bureau']);
}

To rename the item, do this:

function MYMODULE_menu_alter($items) {
  $items['user/%user/bureau']['title'] = 'New Name';
}

and then visit the modules page and submit to rebuild the menu system.
hope that helps.