It is not permissible for a Muslim to pursue a lawsuit under a non-Muslim government, as Allah (Exalted be He) says:
And whosoever does not judge by what Allâh has revealed, such are the Kâfirûn (i.e. disbelievers of a lesser degree as they do not act on Allâh’s Laws).
This is clear and all praise is due to Allah.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.