Unfortunately, that looks to be a string we missed adding to the language file. We're working on 3.1.2, which should be out on in the next day or 2. That string will be added to the language file. If you're in urgent need of changing it, you can find the exact string in the following file:
/components/com_jfbconnect/libraries/facebook.php, line 148
Sorry for the troubles, and thanks for pointing it out!