We updated our Joomla! 1.5 Lab site to Joom!Fish 2.0.1 immediately once it became avalibale. Unfortunately, after the upgrade, we were experiencing problems switching languages.

The mod_jflanguageselection seems to build URLs incorrectly for languages not currently used when SEF is turned on. As a temporary fix, try editing modules/mod_jflanguageselection/helper.php and changing the following lines in function getJFMenu()

            $sql   = 'SELECT m.*, c.`option` as component' .
            ' FROM #__menu AS m' .
            ' LEFT JOIN #__components AS c ON m.componentid = c.id'.
            ' WHERE m.published = 1 '.
            ' AND m.id= '.$activeMenu->id.
            ' ORDER BY m.sublevel, m.parent, m.ordering';

to

            $sql   = 'SELECT m.*, c.`option` as component' .
            ' FROM #__menu AS m' .
            ' LEFT JOIN #__components AS c ON m.componentid = c.id'.
            ' WHERE m.published = 1 '.
            //' AND m.id= '.$activeMenu->id.
            ' ORDER BY m.sublevel, m.parent, m.ordering';

It seems to work well with our installation.