OK, it's DIN. I do not know if DIN to USB adapters exists, can not find on Google.
Theoretically it could work with connecting keyboard to DIN to PS/2 adapter, and then this adapter to a PS/2 to USB adapter, so first this
and then this
. However I refuse to take any responsibility if it does not work.
Worth to think is that those old keyboards might need more power than that a USB port can provide. Anyway, Why don't you just buy a new keyboard? You get a good USB keyboard with the price of adapters you would need with your old one.