Change of validation error message

This is very suitable for someone less experienced contributors.

Thank you for the patch!

-    if ($max !== EntityBrowserElement::CARDINALITY_UNLIMITED && $count > $max) {
+    //If the carinality value is 1 displaying the error message in singular
+    if ($max !== EntityBrowserElement::CARDINALITY_UNLIMITED && $count > $max && $max == 1) {
+      $message = 'You can not select more than %max entity.';
+    }
+    elseif ($max !== EntityBrowserElement::CARDINALITY_UNLIMITED && $count > $max) {
       $message = 'You can not select more than %max entities.';
+    }
+    if (isset($message)) {
       $parameters = ['%max' => $max];
       $violation = new ConstraintViolation($this->t($message, $parameters), $message, $parameters, $count, '', $count);

$this->formatPlural() should be used instead of $this->t(). This is standard way of handling translations of strings that require singular and plural form.

Committed. Thanks!