diff -u b/core/lib/Drupal/Core/Entity/Entity.php b/core/lib/Drupal/Core/Entity/Entity.php
--- b/core/lib/Drupal/Core/Entity/Entity.php
+++ b/core/lib/Drupal/Core/Entity/Entity.php
@@ -184,9 +184,8 @@
     $entity_info = $this->entityInfo();
     if ($entity_info['fieldable'] && field_info_instance($this->entityType, $property_name, $this->bundle())) {
       $field = field_info_field($property_name);
-      // Since we are getting and not setting, we call getFieldLangcode with
-      // strict = FALSE, so if we request a field with a invalid language we
-      // don't throw an exception.
+      // Prevent getFieldLangcode() from throwing an exception in case a
+      // $langcode has been passed and it is invalid for the field.
       $langcode = $this->getFieldLangcode($field, $langcode, FALSE);
       return isset($this->{$property_name}[$langcode]) ? $this->{$property_name}[$langcode] : NULL;
     }
@@ -205,7 +204,7 @@
     $entity_info = $this->entityInfo();
     if ($entity_info['fieldable'] && field_info_instance($this->entityType, $property_name, $this->bundle())) {
       $field = field_info_field($property_name);
-      // This will throw an exception if the $langcode is invalid.
+      // Throws an exception if the $langcode is invalid.
       $langcode = $this->getFieldLangcode($field, $langcode);
       $this->{$property_name}[$langcode] = $value;
     }
@@ -219,31 +218,38 @@
   /**
    * Determines the language code for accessing a field value.
    *
-   * If the entity is language-specific and the field is translatable, the
-   * langcode is used to access the field value. Otherwise,
-   * LANGUAGE_NOT_SPECIFIED should be used to access the field value, as in the
-   * case of a field shared among all language versions of an entity. When the
-   * field is not translatable and the langcode attempted is not
-   * LANGUAGE_NOT_SPECIFIED an exception is thrown in strict mode, or NULL is
-   * returned in non-strict mode.
+   * The effective language code to be used for a field varies:
+   * - If the entity is language-specific and the requested field is
+   *   translatable, the entity's language code should be used to access the
+   *   field value.
+   * - If the entity is not language-specific, LANGUAGE_NOT_SPECIFIED should be
+   *   used to access all field values.
+   * - If a field's values are shared among all language versions of an entity,
+   *   LANGUAGE_NOT_SPECIFIED should be used to access them.
    *
-   * @param $field
+   * There cannot be valid field values if a field is not translatable and the
+   * requested langcode is not LANGUAGE_NOT_SPECIFIED. Therefore, this function
+   * throws an exception in that case (or returns NULL when $strict is FALSE).
+   *
+   * @param string $field
    *   Field the language code is being determined for.
-   * @param $langcode
+   * @param string|null $langcode
    *   (optional) The language code attempting to be applied to the field.
-   * @param $strict
-   *   (optional) Flag for how strict to be, which takes a Boolean TRUE/FALSE
-   *   value. This flag exists so we can be differently strict for invalid
-   *   langcodes when setting and getting field values. When $strict is TRUE,
-   *   an exception is thrown if the field is non-translatable and the langcode
-   *   is anything other than LANGUAGE_NOT_SPECIFIED. When $strict is FALSE,
-   *   NULL is returned instead of an exception being thrown. For example, the
-   *   EntityInterface set() uses $strict TRUE, and the EntityInterface get()
-   *   uses $strict FALSE.
+   * @param bool $strict
+   *   (optional) When $strict is TRUE, an exception is thrown if the field is
+   *   not translatable and the langcode is not LANGUAGE_NOT_SPECIFIED. When
+   *   $strict is FALSE, NULL is returned and no exception is thrown. For
+   *   example, EntityInterface::set() passes TRUE, since it must not set field
+   *   values for invalid langcodes. EntityInterface::get() passes FALSE to
+   *   determine whether any field values exist for a specific langcode.
    *
-   * @return
+   * @return string|null
    *   The langcode if appropriate, LANGUAGE_NOT_SPECIFIED for non-translatable
    *   fields, or NULL when an invalid langcode was used in non-strict mode.
+   *
+   * @throws \InvalidArgumentException
+   *   Thrown in case a $langcode other than LANGUAGE_NOT_SPECIFIED is passed
+   *   for a non-translatable field and $strict is TRUE.
    */
   protected function getFieldLangcode($field, $langcode = NULL, $strict = TRUE) {
     // Only apply the given langcode if the entity is language-specific.
@@ -254,18 +260,20 @@
       return isset($langcode) ? $langcode : $default_language->langcode;
     }
     else {
-      // Field was non-translatable but the attempted langcode was something
-      // other than LANGUAGE_NOT_SPECIFIED.
-      if ($langcode != NULL && $langcode != LANGUAGE_NOT_SPECIFIED) {
-        // Only throw Exception in strict mode.
+      // The field is not translatable, but the caller requested a specific
+      // langcode that does not exist.
+      if (isset($langcode) && $langcode !== LANGUAGE_NOT_SPECIFIED) {
         if ($strict) {
-          throw new EntityStorageException(format_string("Field @field_name is not translatable and only works with langcode = LANGUAGE_NOT_SPECIFIED", array('@field_name' => $field['field_name'])));
+          throw new \InvalidArgumentException(format_string('Unable to resolve @langcode for non-translatable field @field_name. Use langcode LANGUAGE_NOT_SPECIFIED instead.', array(
+            '@field_name' => $field['field_name'],
+            '@langcode' => $langcode,
+          )));
         }
         else {
           return NULL;
         }
       }
-      // Field was non-translatable and the langcode was LANGUAGE_NOT_SPECIFIED.
+      // The field is not translatable and no $langcode was specified.
       return LANGUAGE_NOT_SPECIFIED;
     }
   }