Bitte, Entschuldigung Sie bitte, I suggest you have an affidavit notarized attesting to the transalation of the contract.
While you may argue that the contract meets legal requirements and that it up to the other party to understand what they are signing, having a disclosure providing noitice that the have sufficient time to seek legal advice on the issue, and be correct, they may say they had no idea, that you lied, that the translator did not disclose the facts, etc. and they could get away with it.
Your translator needs to be of legal age and be able to read english and speak the language for the party executing the contract. It should be done in front of a third party or notary.
Now this may not be a requirement, but in doing loans on the secondary market, the mortgage bankers want to see it documented that the borrower understood the transaction and that it was explained to them in their language.
Seien Sie vorsichtig, Bill