Polylang hack for category, tag translation

polylang-hack.php

function before_get_post ($stm) {
    if ($stm->is_category || $stm->is_tag) {
        $term_lang = !empty($stm->query['lang']) ? $stm->query['lang'] : '';

        if (empty($term_lang) ||
            !function_exists('pll_default_language') ||
            ($term_lang === pll_default_language())) {
            return;
        }

        $taxonomy = $stm->is_category ? 'category' : 'post_tag';

        $slug = $stm->is_category
          ? "{$stm->query['category_name']}-{$term_lang}"
          : "{$stm->query['tag']}-{$term_lang}";

        if ($term = get_term_by('slug', $slug, $taxonomy)) {
              if ($stm->is_category ) {
                $stm->query_vars['category_name'] = $slug;
              } else {
                  $stm->query_vars['tag'] = $slug;
                  $stm->query_vars['tag_id'] = $term->term_id;
              }
        }
    }
}

add_action('pre_get_posts', 'before_get_post', 25, 1);

function modify_category_tag_slug($termlink, $term) {
    if ('category' === $term->taxonomy || preg_match('/(post_)?tag/', $term->taxonomy)) {
        return preg_replace('/-en(\/)?$/i', "$1", trim($termlink));
    }

    return $termlink;
}

add_filter('term_link', 'modify_category_tag_slug', 10, 3);

function modify_post_slug( $url, $post ) {
    if ( $post->post_type == 'post' ) {
        $categ_slug = wp_get_post_categories( $post->ID, ['fields' => 'slugs' ] );
        foreach ($categ_slug as $categ_slug ) {
            if ((false !== strpos($url, $categ_slug)) && (false !== strpos($categ_slug, '-en'))) {
                $categ_new_slug = str_replace('-en', '', $categ_slug);
                return str_replace($categ_slug, $categ_new_slug, $url);
            }
        }
    }

    return $url;
}

add_filter( 'post_link', 'modify_post_slug', 10, 3 );

function display_lang($content) {
   $lang_swither_options = [
     'hide_current' => 1,
     'show_flags' => 1,
     'echo' => 0,
     'hide_if_no_translation' => 1
   ];

   if (function_exists('pll_the_languages')) {
      return '<ul class="lang-switcher">' .  pll_the_languages($lang_swither_options) . '</ul>' . $content;
   } else {
     return $content;
   }
}

//add_filter ('the_content', 'display_lang');

add_filter('pll_get_taxonomies', 'add_tax_to_pll', 10, 2);
function add_tax_to_pll($taxonomies, $hide) {
    if ($hide)
        unset($taxonomies['my_tax']);
    else
        $taxonomies['my_tax'] = 'my_tax';
    return $taxonomies;
}

function nirvana_meta_before() {
	global $nirvanas;

	// If single page take appropriate settings
	if (is_single()) {
		$nirvana_blog_show = $nirvanas['nirvana_single_show'];
	} else {
		$nirvana_blog_show = $nirvanas['nirvana_blog_show'];
	}

	// Post Author
	$output="";
	if ($nirvana_blog_show['author']) {
		$output .= sprintf( '<span class="author vcard" ><i class="crycon-author crycon-metas" title="'.__( 'Author ','nirvana'). '"></i>
				<a class="url fn n" rel="author" href="%1$s" title="%2$s">%3$s</a></span>',
				esc_url( get_author_posts_url( get_the_author_meta( 'ID' ) ) ),
				sprintf( esc_attr( __( 'View all posts by %s', 'nirvana' ) ), get_the_author() ),
				get_the_author()
		);
	}

	// Post date/time
	if ($nirvana_blog_show['date'] || $nirvana_blog_show['time'] ) {
		$separator=''; $date=''; $time='';
		if ( $nirvana_blog_show['date'] && $nirvana_blog_show['time'] ) {
			$separator = " - ";
		}
		if ($nirvana_blog_show['date']) {
			$date = get_the_date();
		}
		if ($nirvana_blog_show['time']) {
			$time = esc_attr( get_the_time() );
		}
		$output .= '<span>
						<i class="crycon-time crycon-metas" title="'.__("Date", "nirvana").'"></i>
						<time class="onDate date published" datetime="' . get_the_time('c') . '">
							<a href="' . esc_url( get_permalink() ) . '" rel="bookmark">' . $date . $separator . $time . '</a>
						</time>
					</span>'.
					'<time class="updated"  datetime="' . get_the_modified_date('c') . '">' . get_the_modified_date() . '</time>';
	}

	// Post categories
	if ($nirvana_blog_show['category'] &&  get_the_category_list()) {
		$output .= '<span class="bl_categ"><i class="crycon-folder-open crycon-metas" title="' . __("Categories", "nirvana") . '"></i>'
		. get_the_category_list( ', ' ) . '</span> ' ;
	}

    $lang_switcher = '';
	if (!(is_category() || is_home() || is_archive() || is_front_page())) {
		$lang_switcher = display_lang('');
	}

	echo $output . ' ' . $lang_switcher;
}