The Type-212 is a new design which is smaller and uses more advanced building technology (anti-magnetic steel). On the other hand, the 214 is essentially an upgraded Type-209 which uses the fuel cell AIP of the Type-212. So there is some difference.
There is indeed another great difference between 212 and 214. The South Korean 214 uboats were built by Hyundai Heavy Industries and the Greeks 214 by Hellenic Shipyards. Also the Greeks just don't have the money to pay the boats so they made up these problems. Try some translater on that article: http://www.welt.de/welt_print/wirtschaft/article4587572/HDW-stoppt-U-Boot-Vertraege-mit-Griechenland.html