Any linked resource in a course / learning experience must be fully accessible to learners if it is required for the learner to use the content to complete the course.
Make course elements written in a language other than English machine readable by marking up the part of the text where you use a World Language by creating a language tag with a correct lang attribute in it.
All essential non-text content that is presented to the user has a text alternative that serves the equivalent purpose. In cases of purely decorative imagery, the alt attribute should be left empty (or null) or with a single space in CourseArc.