We go to great lengths to ensure that our pre-Pesach chametz sale is effective according to halacha. Thus, we effect the sale via various means of acquisition: kinyan kesef, kinyan sudar, kinyan agav karka, kinyan chatzer, and hefker bes din. We also write a sales contract, which is halachically effective, Rabbi Chaim Jachter explains, not as kinyan sh'tar, but as a part of the kinyan kesef or as a situmta.
Do we try to ensure that that contract be enforceable according to local (non-Jewish) law, e.g. in secular courts, or is that not important?
I suspect we may, since we're using it as situmta (the way people transact business), and people transact business with enforceable contracts. On the other hand, maybe the form of the transaction (viz, with a contract) is what makes it a situmta and not the details (e.g., enforceability of the contract). (I honestly don't know much about how situmta works.)
One possible relevance of this question is the sales contract in France. In the United States, as far as I know, the contract is written in Hebrew. (The gentile, in most cases at least, cannot read it himself, but it's explained to him and of course he can hire a professional translator if he so desires.) However, I'm told that no contract is enforceable in France unless it's in French.