Thank you very much for your question. For me what is most important is that a royal father speaks and his audience understands him. If he can speak either in Igbo or English and his people understand him is most important.
On the other hand, as custodians of the culture and tradition of the people, it is better they use Igbo language in their official engagements. Now you also suggested that the royal fathers will hire an interpreter. In that case, will you also give them money to hire the interpreters?
Our people like to send the traditional rulers on different assignments without enough support. These royal fathers are not super humans and I hope you know that very well.
Finally, if a royal father can hire an interpreter that will be very good, if he can speak in Igbo fluently, that will also be nice. Let the audience understand their royal fathers.
You know, most of these royal fathers went to school in those days when you would be flogged for speaking in Igbo language. That made them to forget Igbo language a little. If our people or government can support the royal fathers to advance this cause, all our ezes will be happy to use Igbo language officially.