IO.Directory.CreateDirectory doesn't support Chinese?

Hi,

I'm developing an xamarin forms APP, in which I want to create a directory contains Chinese characters, like this:

        var documentsPath = Path.Combine(Android.OS.Environment.ExternalStorageDirectory.Path, "HEBTrain/Documents");
        var path = Path.Combine(documentsPath, "1工段/课件");
        Directory.CreateDirectory(path);

However, only "1工段" was created.
All the source code is in an UTF-8 file, so it should not be related to encoding.
If I change the Chinese string "1工段/课件" to "1Dept/course_ware", then all the directories are created successfully.

Is there any bug in Directory.CreateDirectory?
Why is it not same with the .NET version?

BTW, we sent this question to android@xamarin.com for help about 10 days ago.
Though we purchased business license, we checked our email every day, no response.(How long will it take to answer a question for a business user?)
So I ask it here for luck.