Text dump from Unicode Form and unreadable result

I’m using a php script which I use to generate forms for my students to fill in and mail me hteir home work.
M problem is as follows: My web pages are all UTF-8 encoded because my Students are Chinese and use several languages on the same form. Most if not all of them use different Windows flavors, and probably different flavours of Windows Traditional Chinese ecoding. However I am a Mac User.
No matter how hard I try if they don’t write in English I get mostly garbage.
My PHP form allows me to dump the students work to a file on the server. I download the files to my Mac using FTP but still all I get is garbage unless is English. I am not familiar with protocols and so on, but I am totally unable to read Chinese in these files.
Does anyone have any idea about getting back to UTF-8 these text files, so I can place my forms in FileMaker pro (eventually)?
Thanks a lot