One of the biggest roadblocks as a translator is translating linguistic puns, especially if they're homonym-based jokes or jokes which revolve around compounding two separate words with the same beginning/ending. Since these jokes are based off of how they sound when spoken, translating them into english, an entirely different language, is obviously no simple task.
Sometimes, jokes CAN be translated into english with minimal pun-loss, but for the majority of cases, you're stuck with the choice of dropping the pun, making a completely different pun, or forcing the pun in a somewhat unnatural manner.