The current coding system was introduced sometime around 1990 (give or take 5 years or so, memory fades...) but it is quite similar to the system used before that. The most notable differences was that cloud type used to be given in all cases, also the amount in octas rather than FEW/SCT/BKN/OVC. Weather codes were also prefixed by a two-digit numeric coding which you didn't need to understand unless you were a meteorologist.
I don't see the point of translating into plain language. All pilots from PPL up are required to understand the codes and once you do, interpreting a coded TAF/METAR is much faster than reading a plain language translation.
Personally, I always turn off translation into plain language on any flight planning software I use...
Last edited by AirborneAgain; 3rd November 2013 at 22:52.
Reason: typos...