If an instructor use your own profile with spanish language and grade a submission this will be saved on database in spanish. But, if another instructor with your profile in english language want to see the grade of that submission, he will see in spanish instead of his profile's language.
You can see the patch. This will mean there will be necessary to change scaled_grade property values in database from internationalized values to english 'No grade'. I don't know another form to do it.