mini-DIN is another name for PS2. Even if it's a terminal 'board, you can probably use Soarer's Teensy Terminal (and PS2) to USB with NKRO adapter.
As far as I know, not all the keys will work in a modern OS, but most will. It really depends on the terminal emulation software the keyboard was designed for (for which it was designed).
I would also like to note that this appears to be an ISO layout, judging by the vertical enter and how the angle brackets are on the same key.
Also, mightn't it be an RD?