Thanks for your interest, Stephen. The age-old debate - personally I tend to steer clear of 'nevers' and 'always' when it comes to what is best in teaching situations - these can vary in many ways and dogma can be a real obstacle. Nonetheless, you need to be guided by ideas about what is most beneficial and effective - that's the point of having teachers.
My own guide (we're talking mono-lingual teaching situations here) is that relying on L1 in the classroom is doing learners a disservice, although it's what a fair number of them ask you to do. It can be a lazy short-cut - I think it probably often is - but there are several good reasons not to translate for convenience.
One very practical reason (in the case of English mother-tongue teachers) is that it gives an unfair 'advantage' to teachers who know their students' language well, over their colleagues who don't - and some students might think teachers 'better' or 'worse' as a result. I've observed teachers mis-translate words in class - another good reason for the practice to be discouraged. It's also true that while some students want translation, many others dislike it - they find it de-motivating and a waste of valuable time.
From a learning point of view, regular use of translation doesn't do learners a favour - it teaches them a 'shallow' relationship with the new language, and although lessons will seem 'easier' it will make out-of-classroom interaction in the the new language more 'laborious' and stressful. There's also the fact that some things simply don't translate - this applies both for lexis and grammar.
However ........ translating new words can be a lazy shortcut, but refusing to do so can become a very long and circuitous diversion - like eating a kilo of celery to gain just a handful oif calories (I like celery but it's not a good source of energy). Lesson time is limited - a talented and perceptive teacher can often get meaning across economically and effectively - but in many 'no-translation at any cost' classrooms there's a lot of time and frustration before mission is accomplished (often by classmates whispering the translation anyway).
Do I translate? Yes - sometimes. At beginner level with new classes I will use some Italian (when I'm teaching Italian students - or Italian-speaking students, as is the case here), although not to teach the language content but to give little interludes of advice and information about what we are learning. I like to give a brief outline of the course and about what lessons will involve, and maybe to remind students about how things are going from time to time.
I often point things out about English - unlike some languages it has no genders: "wow, that's easy!" - and what sort of things are difficult and take everyone time to begin to grasp. So, I translate for 'welfare' reasons rather than as a teaching tool. Sometimes students check with you that they have understood something - I acknowledge these 'translation for confirmation' requests, rather than pretend not to understand.
One other thing (this is much longer than I'd expected). Translation is a useful skill and I try to do short spontaneous translation activities - with elementary and first-intermediate levels. When we read short dialogues (phone-calls are good), I might also ask for an off-the cuff translation - not word-by-word but just what was said.
This is a real-life need - it's not unusual to have to report and translate a phone-call or e-mail, or translate for a friend in a social setting. This is a useful and enjoyable translation activity to sprinkle in to lessons. It has to be quick, so accessible content is required.
