Programming language design is often thought of in terms of which features you include.
【翻译】编程语言设计通常是根据所包含的什么样的特性来考虑的。
1. think of  sth.= think about sth.：考虑某事
本句是被动语态：be thought of 被考虑
 2. in terms of = according to 根据；依据

所以，of  跟 think 有关，跟 in terms of 无关。of  的宾语是被动语态的主语。