Actually, the translation file already has the translation for the “Continue reading” text. I just tried it on my local server and the translation displays properly on my end.
Try downloading the theme’s latest language pack here:
http://www.khairul-syahir.com/wordpress-dev/graphene-theme#languages
Scroll down after the list of languages the theme is available in, and you should see a download link for the latest language pack, along with the instruction on how to use it.