Multilingual classes are EFL or ESL classes made up of students from different countries and who do not share a common mother tongue. They are the typical format at language schools in English-speaking countries.
Although many of the teaching techniques and exercises are common to those used in monolingual classes, one of the main points the teacher needs to take into consideration is that even if he/she speaks other languages, out of respect for the other students, the teacher must avoid showing any kind of favouritism by "helping" students in their mother tongue.
As English is the only common language between the learners, students in multilingual classes inevitably make more use of the target language, both in and out of class.
Teachers might like to ensure that for exercises involving pairwork, for instance, students who share a mother tongue are separated.