How can I politely explain to my students that the texts in my course are all in English and it is their duty to read it nonetheless?

Eventually I grew tired of having to explain over and over why all my class material is in English. It's a mandatory course in Art History. I want to put some warning in my syllabus to minimize any arguments. The problem is how to do it politely, yet clearly.

The reasons are clear: there is no material in their native language for the courses I teach; obviously I cannot and will not translate the material; and it is their duty to read in English. I guess I cannot tell them straight that if they do not read English well they will not even understand classes well and will get low grades. I don't want to sound rude.

Is there a way to explain the situation, or is it better not to include such a written statement in a syllabus and keep things as they are?

I agree that it makes sense to set expectations as early as possible.

I'd just put

Note that all XXX for this course are in English.

in the syllabus. You should of course be specific as to what XXX is:

• Class slides
• Required reading
• Supplemental reading
• Lectures (you could have slides in English but speak the local language during the actual lecture)
• Quizzes
• Exams

If quizzes/exams are in English, you should also note whether students would be expected to answerin English.

Whether or not you also want to include the reasons for this is really up to how much space you have in the syllabus and whether there isn't anything more important to put there. I'd say that a warning might be a better use for the space:

If your English is not up to reading/understanding/writing technical documents, this course likely is not a good fit for you.