“变得乡气”可以翻译为“become rustic” 或 “take on a countrified/rustic look/air” 。
“rustic”有“乡村的；质朴的；粗野的”等含义， “become rustic”直接表达变得具有乡村那种质朴甚至可能略带土气的风格； “take on a countrified/rustic look/air” 侧重于描述呈现出一种乡村式的外貌或气质 。例如：
After living in the countryside for a long time, he started to become rustic.（在乡下住了很长时间后，他开始变得乡气了 。 ）
The old house, after years of neglect, had taken on a countrified air.（这座老房子多年无人照管，开始呈现出一种乡气的样子 。 ）