"开朗"用英语可以表示为 "cheerful" 或 "sunny".
"Cheerful" 来源于中世纪英语词 "cherful"，其意思是 "快乐的" 或 "愉快的". 例句：
She's always so cheerful, even on rainy days. (她总是那么开朗，即使在雨天也是如此。)
The cheerful music put everyone in a good mood. (开朗的音乐让每个人都心情愉悦。)
"Sunny" 来源于中世纪英语词 "sunne"，其意思是 "阳光明媚的" 或 "快乐的". 例句：
It's a sunny day, let's go for a walk. (今天天气阳光明媚，让我们出去散步吧。)
His sunny disposition always brightened up the room. (他阳光明媚的性格总是给房间带来温暖。)