Translating a site where default is in two languages
When you pass string through t() without specifying a langcode, then it will default back to English.
So, if string is a French word, it will be handled as an English word.

Two options:


Always use English words in t() and use the translate interface to
translate it to French. 
As per https://api.drupal.org/api/drupal/includes!bootstrap.inc/function/t/7
set the langcode as such t($string, $args = array(), $options =
array('langcode' => 'fr'))