不了解某人英文

I am not acquainted with sb

I'm not familiar with him.或者你说的也对的I don't know her.也是正确的~~~~~~~~`

no idea about sb.know little about sb.

为你细细讲解：A be unfamiliar to B是指：A对B而言是陌生的事物，B感到陌生。A be unfamiliar toB是指：A不了解B，A感到陌生。某人对某人不熟习，假如是吉姆对马克不熟系（吉姆不认识马克）则可以表达为：Jim is unfamiliar with Mark.或Mark is unfamiliar to Jim.希望帮助到你！