Issue #1831636 by claudinec, jlscott, thsutton, chrischinchilla, moe4715,...

Issue #1831636 by claudinec, jlscott, thsutton, chrischinchilla, moe4715, ancamp, YesCT, kbasarab: Reword error message about incompatible translation formats.

core/modules/translation_entity/translation_entity.module

@@ -847,7 +847,7 @@ function translation_entity_language_configuration_element_validate($element, ar
     // @todo Set the correct form element name as soon as the element parents
     //   are correctly set. We should be using NestedArray::getValue() but for
     //   now we cannot.
-    form_set_error('', t('Translation is not supported if language is always one of: @locked_languages', array('@locked_languages' => implode(', ', $locked_languages))));
+    form_set_error('', t('"Show language selector" is not compatible with translating content that has default language: %choice. Either do not hide the language selector or pick a specific language.', array('%choice' => $locked_languages[$values['langcode']])));
   }
 }