Drupal.t('Select a page') is not translated into another language (mobile menu) after clearing cache and translating strings through the translation menu. What should be added or changed to get translation?

var settings = {
    combine: true,  //combine multiple menus into a single
select
    groupPageText: 'Main',  //optgroup's aren't selectable, make an option for it
    nested: true,                   //create optgroups by default
    prependTo: 'body',              //insert at top of page by default
    switchWidth: 480,               //width at which to switch to select, and back again
    topOptionText: Drupal.t('Select a page')    //default "unselected" state
},