他是困难的但是有趣用英语怎么说

这句话的英文表达是 "He is challenging but fun."
challenging 表示困难的，来源于动词 challenge，意为挑战。
fun 表示有趣的，来源于名词 fun，意为娱乐。
例句：
Climbing that mountain was challenging, but it was also a lot of fun.
(爬那座山很困难，但是也很有趣。)
The math exam was challenging, but I found it fun to solve the problems.
(数学考试很难，但是我觉得解题很有趣。)