(based on Shoel U’meishiv II:II:79)

Case: Reuven lent Shimon 200 rubles with a loan document. When it came time to pay, Shimon refused not only to pay but to come before the local beit din. Reuven then sued him in non-Jewish court, which required an outlay of money, and won, but Shimon went to criminal court with lies about Reuven. All this did not help Shimon, and the courts made him pay the principal and expenses. At this point, Shimon turned to beit din and complained that Reuven had taken him to non-Jewish court without a shtar seiruv (a document of beit din that sanctions he who refuses to submit to beit din and allows the other side to turn to the courts). Reuven countered this with two claims: beit din did not write a shtar seiruv because Shimon is a violent person. Secondly, since there is an authorized loan contract, there is no need for real adjudication, so that Shimon’s refusal to pay justifies going directly to the non-Jewish courts.

Ruling: Regarding the claim that it is permitted to go non-Jewish courts to extract payment that is chronicled in a certain type of document, the S’ma (61:14) does say something of that nature. However, the Taz (ad loc.) disagrees. In fact, even the S’ma only spoke about a case where the document explicitly states that he can extract money directly through the courts.
If, though, a shtar seiruv was not written because it was clear that it would not be of help, as it seems by his later aggressive behavior, then Shimon is responsible for the results of Reuven needing to go to the courts. Even though the Rama (Choshen Mishpat 26:1) prefers the opinion that whoever goes to non-Jewish court is not helped by beit din even if that litigant was correct, the Tumim (26:2) argues with him. In any case, the Rama is talking about a case where he did not go at all before beit din, whereas here Reuven approached beit din, and his behavior was justified by both beit din and the courts. Therefore, Shimon should be responsible to pay for the expenses related to the non-Jewish courts.
Even if Reuven is claiming ribbit from Shimon, if he had a heter iska, then he is allowed to receive not only the planned interest/profit, but even that which corresponds to the period that Shimon kept the money instead of giving it back.
It is possible to corroborate the above conclusion by means of another piece of logic, although it is a very novel idea. If the document was written in such a way that it could have been sold to a non-Jew and the latter could of course have gone to the non-Jewish courts, it is as if he obligated himself to be held to the rules of those courts. [The Shoel U’meishiv applied this rule to answer certain questions, but he was troubled by the question of how far the idea can be taken without compromising the rule of being required to go to beit din.]