How to translate it?
He always asks after you in his letters. 是"他总在信里问候你"的意思吗?and what does "after"mean ?

Question

Answer

ask after you :询问你的一些情况。当然也是问候的意思。  这里的after是作为介词使用，“有关、关于”的意思。

Answer

he alwais ask about you, about you're well been, he whant's to know how are you ...

Answer

The phrase 'asks after you' means the person is asking about you, how you are, what you're doing, etc.