Of course they can, but it takes time. You have to explain cultural contrasts and culture bound concepts.
If we as teachers, are terrified by the fact that students MIGHT think we are not knowledgeable enough to answer every question, we are going to face many problems.
You should make them familiar with this notion and also teach them the fact that they can use internet to check for idioms, words, etc. So whenever they come up with such questions, you can simply tell them, "Well this is a culture bound concept, there's no such concept in their language/society. If you think I am wrong go google it and bring the class the result."
All this said, it depends on their age group. For children you must have better tricks up your sleeve, whereas for adults, you simply ought to be frank and straight forward. Just tell them there's no such word! Go find it if you can... and make them more familiar with the target culture/language. Language is a package! don't forget it!
This makes you feel much better facing some issues, and makes your students more autonomous. Students' autonomy is our goal after all!
Hope you don't mind my long winded answer....