Question for Upgrade to 3.4 from 3.3.6 multilanguages Site - Joomla! Forum - community, help and support

the site build joomla 2.5.0, , has been upgraded since, until current 3.3.6. without issues, upgrade joomla 3.4 , encounter following error:-
success warning:-

an error has occurred:-

1062 duplicate entry '0' key 'primary' sql=insert `xyz_postinstall_messages`
(`extension_id`, `title_key`, `description_key`, `action_key`, `language_extension`, `language_client_id`, `type`, `action_file`,
`action`, `condition_file`, `condition_method`, `version_introduced`, `enabled`) values (700, 'com_cpanel_msg_robots_title',
'com_cpanel_msg_robots_body', '', 'com_cpanel', 1, 'message', '', '', '', '', '3.3.0', 1);

which returns front end results following text:-

the page isn't redirecting properly

firefox has detected server redirecting request address in way never complete.

problem can caused disabling or refusing accept cookies.

i have made correction following joomla forum view topic - redirect loop error??? http://forum.joomla.org/viewtopic.php?f=707&t=874568
result:- site comes without loop problem. however, encounter incorrect behavior of site:-

the language switcher lost it's menu association ability link menu, instead, once click on flag list menus of languages in 1 page number o or 1 or 2 @ end of each menu name.

any 1 have solution? appreciated.

1. first fix database (extension manager=>database->fix)
2. make sure languagefilter plugin enabled
3. check home pages set every language , rebuild menus