The word law in Arabic has several synonyms as below:

تشريع = Tashree'e
الحقوق - قانون = Al-Hoqooq - Qanoon
دستور = Dostoor
شريعة = Shari'ah
ضابط = Dhabet
ناموس = Namoos
نظام = Nidham

You have no way except to call it Law "Qanoon". There is a dispute among the jurists on this point. The majority of them hold that International Law is not law in the true sense of the term as there is no sanction behind it for its enforcement, therefore, it is not called law. At the most it can be termed International Morality or if it is called law it is termed as such as a matter of curtesy.

There are some jurists who opine that it is law as there are sanctions behind it like iinternational public opinion and sanctions of the Security council, however, it has been proved that the might never care for international public opinion or any sort of sanctions or resolution of any international organization.

You will have to call the Internation Law for Human Rights as "Law" because world terms it like that and if you wanted to choose any other term for that people would not understand it.