that really depends on the size of the barrier. I once was asked to give instructions to a couple from Ukraine who only spoke Russian. In that case, their daughter was there to translate. I probably could have gotten them to do the techniques but it was important to me to explain the ‘Why’ behind the ‘What’, and that would not have worked in any other way.
Otherwise, I believe that, with exaggerated demonstrations, you can train somebody without speaking the language.