question moving MDL-21195 add missing error message strings.

lang/en/question.php

@@ -121,6 +121,8 @@
 $string['exportquestions'] = 'Export questions to file';
 $string['exportquestions_help'] = 'This function enables the export of a complete category (and any subcategories) of questions to file. Please note that, depending on the file format selected, some question data and certain question types may not be exported.';
 $string['exportquestions_link'] = 'question/export';
+$string['filecantmovefrom'] = 'The questions files cannot be moved because you do not have permission to remove files from the place you are trying to move questions from.';
+$string['filecantmoveto'] = 'The question files cannot be moved or copied becuase you do not have permission to add files to the place you are trying to move the questions to.';
 $string['filesareacourse'] = 'the course files area';
 $string['filesareasite'] = 'the site files area';
 $string['filestomove'] = 'Move / copy files to {$a}?';