Task International private law

Task. Hungarian citizen T. gave birth to a daughter, unmarried, from Russian citizen M., who was in Hungary on a long business trip. Some time later, when M. left for Russia, where he was subsequently convicted of theft and sentenced to imprisonment, T. turned to him with a demand to pay her child support. M. refused to pay her alimony obligations, and T. decided to go to court.
Which state´s legislation should the court apply when considering a case? How will the case be resolved if M. goes to a Russian court? If the claim of citizen T. is satisfied, how will the payment (withholding) of citizen M.’s alimony obligations be carried out?