Use CSL for short citations.

bibcite_footnotes.module

@@ -202,9 +202,13 @@ function bibcite_footnotes_preprocess_bibcite_footnote_link(&$variables) {
 
   $title = trim(strip_tags(render($citation_data)));
   $url = Url::fromUserInput('#' . $fn['fn_id'], ['attributes' => ['id' => $fn['ref_id'], 'class' => $class, 'title' => $title]]);
-  
 
-  $link = Link::fromTextAndUrl($fn['value'], $url)->toRenderable();
+// We need to delete the cached markup to render it in a different mode.
+  unset($citation_data['#markup']);
+  unset($citation_data['#children']);
+
+  $citation_data['#data']['mode'] = 'citation';
+  $link = Link::fromTextAndUrl(render($citation_data), $url)->toRenderable();
   unset($variables['fn']['fn']);
   $variables['fn']['fn'] = $link;
 //  $variables['fn']['fn'][] = $link;

src/Plugin/BibCiteProcessor/CiteprocPhpInline.php

@@ -0,0 +1,73 @@
+<?php
+
+namespace Drupal\bibcite_footnotes\Plugin\BibCiteProcessor;
+
+use AcademicPuma\CiteProc\CiteProc;
+use Drupal\Core\Config\ConfigFactoryInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\bibcite\Plugin\BibCiteProcessorBase;
+use Drupal\bibcite\Plugin\BibCiteProcessorInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Defines a style provider based on citeproc-php library.
+ *
+ * Extended to support inline citation links based on the CSL.
+ *
+ * @BibCiteProcessor(
+ *   id = "citeproc-php",
+ *   label = @Translation("Citeproc PHP"),
+ * )
+ */
+class CiteprocPhpInline extends BibCiteProcessorBase implements BibCiteProcessorInterface, ContainerFactoryPluginInterface {
+
+  /**
+   * Config factory service.
+   *
+   * @var \Drupal\Core\Config\ConfigFactoryInterface
+   */
+  protected $configFactory;
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('config.factory')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, ConfigFactoryInterface $config_factory) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+
+    $this->configFactory = $config_factory;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDescription() {
+    return $this->t('Render citation by citeproc-php library');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function render($data, $csl, $lang) {
+    $cite_proc = new CiteProc($csl, $lang);
+    $mode = !empty($data['mode']) ? $data['mode'] : NULL;
+
+    if (!$data instanceof \stdClass) {
+      $data = json_decode(json_encode($data));
+    }
+
+    return $cite_proc->render($data, $mode);
+  }
+
+}