@BritannusRomae Protestants were historically also called 耶稣教 (Yēsūjiào) aka “Religion or the Teaching of Jesus.” Modern terms are 新教 (“New Teaching”) and 基督教新教(Jīdūjiào Xīnjiào). 基督教 (Jīdūjiào) means “Religion of Christ” and often specifically means Protestantism in China.
In Chinese, there are two main terms used for the Pope: 教宗 (Jiàozōng) and 教皇 (Jiàohuáng).
教宗 can be understood rather literally as “Supreme Head of the Religion.”
There is also 教皇 (Jiàohuáng) which is “Emperor of the Religion” or “Religious Emperor.”
教皇 (Jiàohuáng) has long been used as a term of “Pope,” particularly in general secular writing and historically in mainland China. However, Catholic Chinese usage often prefers 教宗, partly because 皇 can misleadingly suggest that the Pope is an emperor in the political sense.