How to get a term from the translated term name?
You can try to translate it before pass it to taxonomy_get_term_by_name function, try some thing like

$string= 'De Lema'; // string in not default site language I suppose in French
$default_lang_short = 'un'; // I supposes you default site language is english change it to your default
$en_value = t($string, array(), array('langcode' =&gt; $default_lang_short));
taxonomy_get_term_by_name($en_value);