Speaking English to them, even if they don't answer in English, is still beneficial because they will be hearing English and have, at least, to understand to reply. There are many arguments for using translation with vocab items with a monolingual class, though I would use it where it is ore efficient rather than as a n easy way out. Where possible, I would recommend trying to explain in English, then using translation as a back-up. however, translation can be useful-imagine trying to explain, say, different types of fish- it would be much quicker and more accurate to give a translation rather than trying to explain the difference between a herring and a trout.
