agaric-coop/web/themes/custom/agarica/agarica.theme

<?php

use Drupal\block\Entity\Block;
use Drupal\Core\Entity\EntityInterface;
use Drupal\Core\Url;

/**
 * Implements hook_preprocess_region__footer().
 */
function agarica_preprocess_region__footer(&$variables) {
  $block = Block::load('languageswitcher');
  $block_content = \Drupal::entityTypeManager()
    ->getViewBuilder('block')
    ->view($block);
  $variables['language_switcher'] = $block_content;
  $variables['language_switcher_link'] = agarica_languague_switch_link();
}

/**
 * Provides a link to switch to another language.
 */
function agarica_languague_switch_link() {
  $derivative_id = 'language_interface';
  $route = \Drupal::getContainer()->get('path.matcher')->isFrontPage() ? '<front>' : '<current>';
  $current_language = \Drupal::languageManager()->getCurrentLanguage($derivative_id)->getId();
  $links = \Drupal::languageManager()->getLanguageSwitchLinks($derivative_id, Url::fromRoute($route))->links;
  $links['en']['title'] = 'Browse this site in English';
  $links['es']['title'] = 'Consulta este sitio en Español';
  $lid = ($current_language == 'en') ? 'es' : 'en';
  // Remove current language from the links
  unset($links[$current_language]);

  // Check if the current path  display an entity.
  $entity = FALSE;
  foreach (\Drupal::routeMatch()->getParameters() as $param) {
    if ($param instanceof EntityInterface) {
      $entity[] = $param;
    }
  }

  // Remove links if the content hasnt' been translated yet.
  if ($entity) {
    $has_translation = (method_exists($entity[0], 'getTranslationStatus')) ? $entity[0]->getTranslationStatus($lid) : FALSE;
    $this_translation = ($has_translation && method_exists($entity[0], 'getTranslation')) ? $entity[0]->getTranslation($lid) : FALSE;
    $access_translation = ($this_translation && method_exists($this_translation, 'access') && $this_translation->access('view')) ? TRUE : FALSE;
    if (!$this_translation || !$access_translation || $current_language == $lid) {
      unset($links[$lid]);
    }
  }

  $links_render_array = [];
  // Transform the links to arrays that can be renderer.
  foreach ($links as $language => $link) {
    $links_render_array[] = [
      '#type' => 'link',
      '#url' => $link['url'],
      '#title' => $link['title'],
      '#options' => [
        'language' => $link['language'],
      ],
    ];
  }

  return $links_render_array;
}