I use the Apple II disk server to make disks for my Plus; the one you'd want would be the DOS 3.3 image on the top there, but given you don't trust your Plus definitely make your DOS 3.3 disk with ADTPro on the IIc instead. (I'm sure you'll have no problems finding the one in the usual places.)
Just for a sanity check, could you post a picture of the interior of the system with the language card in place? Since you're missing at least the one cable I've vaguely wondering if there could be a problem with how your language card is set up. Just for sanity's sake: There should be a 16 pin jumper cable running from the card to the motherboard, plugged in in place of one of the 24 16k RAM chips. That all looks good, everything's seated properly?