Upvote:2
The German Federal Centre for Health Education offers donor cards in many languages specifically for this purpose. They do warn that the local rules apply by default (GrundsΓ€tzlich gilt immer die Regelung des jeweiligen Landes) but they claim the card would generally be honored.
Beyond the implementation details (opt-in, opt-out, central register or not, etc.) the rules generally give a strong weight to the wishes of the deceased. It does therefore make sense that carrying a document expressing those wishes unambiguously in the local language would make it more likely that your organs would be used following your instructions.