Instead of looking for the same in the source code, pls use the translation file in the languages directory to change the Read More string to what you desire. You can use the language file for your language located there or create your own.
You can learn from http://www.solostream.com/blog/tutorials/translate-wordpress-theme/ about translating your site into your language. Pls make sure you add the entry for your language into wp-config.php file like this –
define ('WPLANG', 'fr_FR');
Pls use the pot files in ‘appdev/languages’ folder as a template to create .po files. http://www.poedit.net/ -Poedit is the popular free editor for creating .po and the corresponding binary .mo files.
You may need to do an update in POEdit to see all the strings. Do reach out to us in case you find something that is not translation ready.