add_filter( 'tm_google_fonts', '_jx_add_google_fonts' );
function _jx_add_google_fonts( $fonts ) {
    $fonts['Spectral'] = array(
        'styles'        => '300italic,400italic,600italic,700italic,800italic,400,300,600,700,800',
        'character_set' => 'latin,vietnamese,latin-ext',
        'type'          => 'serif',
    );
    return $fonts;
}