The commands below work to add/change text for the related navigatin bar buttons

$.jgrid.nav.addtext = "Add";
$.jgrid.nav.edittext = "Edit";
$.jgrid.nav.deltext = "Delete";
$.jgrid.nav.searchtext = "Search";
$.jgrid.nav.refreshtext = "Refresh";
$.jgrid.nav.viewtext = "View";

But how do I change navigation button text for the PDF and CSV buttons?

These don't work:
$.jgrid.nav.export_pdf = "REPORT 1";
$.jgrid.nav.pdf = "REPORT 2";