What's brutal about Chinese for a native speaker of English is phonemic tone for speech and lack of cognate vocabulary, coupled with a writing system that reflects a stage of development of writing from 2,000 years ago. But what is forgiving about Chinese is that the grammatical relationships are mostly shown by word order and function words, as in English, rather than by inflection of words. That, to me at least, makes speaking Chinese "easier" than speaking Russian, even though Russian is much more cognate with English.
Arabic may be especially difficult (even as compared to Hebrew, a language I have studied much more) because the standard form of the language is so divergent from the day by day vernacular forms, as noted by a more informed participant who has kindly posted another comment.
The United States federal government language proficiency rating system attempts to identify equal levels of real-world functional proficiency for ratings of interpreters and the like. When I was last tested, the rating scale went from 0 (with a readily apparent meaning) to 5 (a rating in principle reserved for educated NATIVE speakers of the language) in the functional domains of speaking, listening, reading, and writing. I was quite proud of my 4+ rating in speaking and listening to Modern Standard Chinese, but I took quite a few years out of my life to get to that level, as have most westerners I have ever met who have done the same.