Here was my technologically simple solution. Whenever I taught a lower level class I handed out a piece of paper with a short message translated into the first language of the student (I had collected these translations from advanced students and native speakers alike). The message said something like this:
"Hello! This message is in your language because I want you to know what we will do for the first activity. All of the students are reading the same message in their own language. This will be the only message that you get from me in your language."
What do you think was written in the rest of the message?