“a plum in one's mouth”别理解成“一个李子在你嘴里”，而是说话像上层社会一样，有英国上层阶级口音。

【例句】
She had elocution lessons as a child and as a result now speaks with a plum in her mouth.
她小时候上过口才课，结果现在说话时像一个上层社会一样。

While she does not talk with a plum in her mouth, she is very articulate.
虽然她说话不像上层社会一样，但口才很好。