Use placeholder if nothing selected.

Closes #3474966

js/select2-multi-check.js

 (function ($, Drupal, drupalSettings) {
   Drupal.behaviors.select2MultiCheckboxes = {
     attach: function (context) {
-      $(".select2-multiple").select2MultiCheckboxes({
-        templateSelection: function (selected, total, context) {
-          return Drupal.t("Selected @selected of @total", {
-            "@selected": selected.length,
-            "@total": total
-          });
-        },
+      $(".select2-multiple").each(function () {
+        let $item = $(this);
+        $item.select2MultiCheckboxes({
+          templateSelection: function (selected, total, context) {
+            if (selected.length === 0) {
+              return $item.data('select2Config').placeholder;
+            }
+            else {
+              return Drupal.t("Selected @selected of @total", {
+                "@selected": selected.length,
+                "@total": total
+              });
+            }
+          }
+        });
+        // placeholder: this.attr('placeholder'),
       });
-      $(".select2-single").select2MultiCheckboxes({
-        templateSelection: function (selected, total, context) {
-          if (typeof (selected) == "object") {
-            return Drupal.t("Selected @selected of @total", {
-              "@selected": selected.length,
-              "@total": total - 1
-            });
-          } else {
-            return Drupal.t("Selected @selected of @total", {
-              "@selected": 1,
-              "@total": total - 1
-            });
+      $(".select2-single").each(function () {
+        let $item = $(this);
+        $item.select2MultiCheckboxes({
+          templateSelection: function (selected, total, context) {
+            if (typeof (selected) == "object") {
+              if (selected.length === 0) {
+                return $item.data('select2Config').placeholder;
+              }
+              else {
+                return Drupal.t("Selected @selected of @total", {
+                  "@selected": selected.length,
+                  "@total": total - 1
+                });
+              }
+            }
+            else {
+              return Drupal.t("Selected @selected of @total", {
+                "@selected": 1,
+                "@total": total - 1
+              });
+            }
           }
-        },
+        });
       });
       // Get the widget width for elements with multiple selections.
       $(".select2-multiple + .select2-container").each(function(index){