Yes, it is natural to say "someone's face remains unemotional". I have never seen the metaphor of "a windless lake" describe that, but it is poetic and easily understood. Your sentence, "His face remains..." is a good sentence except that you should say "ON a windless day". You are right, it is not beautiful in English. Poetry seldom travels well. I'm no poet, but I'll try. I'm using some unusual words, but you asked me to be poetic: "His aspect abode, devoid of any affect whatsoever, as if becalmed on the waters of a vast lake, his sails floundering in the sun."

Replace “void…whatsoever” with “aspect void”

Your expression in English is understandable, but it can be refined for a more natural and elegant flow. Here's a revised version: "His face remains unemotional, akin to a tranquil lake on a windless, sunny day—stunning yet mysterious." This version maintains the essence of your original expression but is crafted to flow more smoothly in English. Feel free to adjust it further based on your preferences and the context in which you're using it.

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