I'm writing to enquire about language courses.

特此致函询问有关语言课程事宜。

I called the station to enquire about train times.

我打电话到车站询问了火车时刻。

I am writing to enquire about...

我写这封信，想询问关于…的信息。

I am writing to enquire about...

我写信想询问关于…的信息。

Can I enquire about the accident?

能否请问这次事故的情况？