GP Custom next/prev text

if ( ! function_exists( 'generate_content_nav' ) ) :
/**
 * Display navigation to next/previous pages when applicable
 */
function generate_content_nav( $nav_id ) {

    global $wp_query, $post;

    // Don't print empty markup on single pages if there's nowhere to navigate.
    if ( is_single() ) {
        $previous = ( is_attachment() ) ? get_post( $post->post_parent ) : get_adjacent_post( false, '', true );
        $next = get_adjacent_post( false, '', false );

        if ( ! $next && ! $previous )
            return;
    }

    // Don't print empty markup in archives if there's only one page.
    if ( $wp_query->max_num_pages < 2 && ( is_home() || is_archive() || is_search() ) )
        return;

    $nav_class = ( is_single() ) ? 'post-navigation' : 'paging-navigation';
    ?>
    <nav role="navigation" id="<?php echo esc_attr( $nav_id ); ?>" class="<?php echo $nav_class; ?>">

        <?php if ( is_singular( 'post' ) ) : // navigation links for single posts ?>

        <?php elseif ( is_singular( 'programpage' ) ) : ?>

            <h6 class="screen-reader-text"><?php _e( 'Post navigation', 'generatepress' ); ?></h6>
            <?php if ( get_field( 'lesson_links' ) == 'next_only' ):
                // null
                else:
                previous_post_link( '<div class="nav-previous">%link</div>', '<span class="lesson-nav">Previous</span>' );
                endif; ?>
            <?php if ( get_field( 'lesson_links' ) == 'previous_only' ):
                // null
                else:
                next_post_link( '<div class="nav-next">%link</div>', '<span class="lesson-nav">Next</span>' );
                endif; ?>

        <?php elseif ( $wp_query->max_num_pages > 1 && ( is_home() || is_archive() || is_search() ) ) : // navigation links for home, archive, and search pages ?>

            <?php if ( get_next_posts_link() ) : ?>
            <div class="nav-previous"><span class="prev" title="<?php _e('Previous','generatepress');?>"><?php next_posts_link( __( 'Older posts', 'generatepress' ) ); ?></span></div>
            <?php endif; ?>

            <?php if ( get_previous_posts_link() ) : ?>
            <div class="nav-next"><span class="next" title="<?php _e('Next','generatepress');?>"><?php previous_posts_link( __( 'Newer posts', 'generatepress' ) ); ?></span></div>
            <?php endif; ?>

            <h6 class="screen-reader-text"><?php _e( 'Post navigation', 'generatepress' ); ?></h6>
            <?php the_posts_navigation(); ?>
            <?php do_action('generate_paging_navigation'); ?>

        <?php endif; ?>

    </nav><!-- #<?php echo esc_html( $nav_id ); ?> -->
    <?php
}
endif; // generate_content_nav