Is there any suspicion of unlawfulness in translating a book on Zaydi Fiqh and receiving financial compensation for it?

If the book is permissible to translate and publish, then there is no harm in taking a fee for its translation, based on the words of the Messenger of Allah, peace and blessings be upon him: "Indeed, when Allah forbids a thing to a people, He also forbids to them its price."

Since the jurisprudential branches of the Zaydi school do not contradict the general framework of the Sunni schools of thought, there is no harm in translating this jurisprudence and taking a fee for it.