她对他开朗、坚定地一笑，但笑得有点不自然。She gave him a bright, determined smile which seemed unnatural.肉嚼不烂，酱汁黏稠，味道也不自然。The meat was chewy and the sauce was glutinous and tasted artificial.他的笑声好像有点不自然。His laughter seemed a little strained....

“不自然”的英语可以翻译为：[医] self-consciousness，artificiality，artificialness，theatricality ...