After update to Latest Joomla 3.4, K2 components and it's module display wrong language code.
Search module show (SEARCH_ME) & Contact form from K2 component show Like NAME_LABEL_CONTACT, EMAIL_LABEL_CONTACT, K2_SUBMIT_YOUR_COMMENT..., instead of Language.

I decide to upgrade to Joomla 3.5 beta 3, but problem still there. Any help please????

This issue is not related to Joomla!.
These language strings you are seeing are not a part of K2's core templates. This means that your template does not load the required language files.
You need to address this issue to the template's developer.