Would you please speak something about your family?为什么不能用spe

talk about 是固定搭配
talk和speak的区别是
1、speak和talk通常用作不及物动词,都有“说话”的意思.在会议上正式发言用speak,其名词为speech
I know of the man,but I've never spoken to him.
我知道这个人,不过从来没有和他说过话.
He spoke at the meeting.
他在会上发言了.
2、：speak在用作及物动词时,其宾语一般是语言或词语之类的词
He speaks English very well.
他的英语说得很好.
He didn't speak a word.
他一句话也没说.
3、随便漫谈用talk,其名词亦为talk
Human beings can talk,but animals can't.
人会说话,而动物却不会.
They have been talking since two o'clock.
自从两点钟到现在他们一直在谈话.
希望可以帮到你,有不懂的还可以问我^^

用： talk sth. about 固定搭配
speak 经常后跟语言，如： speak English
或电话用语： May I speak to..