contax 50 mm 1.4 lens

The "G" at the end denotes the country of origin...in this case made in Germany. If it is a "J" it was made in Japan.

I can't recall the exact details for the MM but I think it has to do with ttl metering modes.
The MM is compatible with TTL and was a later version than the AE.
All these are T* lenses.

As far as I know all Zeiss lenses with the C/Y mount will work with all Contax 35mm SLRs. The MM lenses work in Shutter, Program, Aperture, and Manual exposure modes, and can be identified by a green number on the aperture ring. The non-MM lenses will work properly in Aperture and Manual exposure modes; no idea what they do in Shutter or Program.

If you're finding the 50 1.4 a bit pricey, go for the 50 1.7; much cheaper and seems just as good.

Carl Zeiss Planar 50mm/1.4 lens for Contax 139,Contax 159,Contax 167, Contax RTS, Contax S2/S2b. 6 element double Gauss design

T* denote Carl Zeiss multicoated

All of them are T*, by the way - denotes proprietary Zeiss multicoating, as Martin says.

As Martin and Soeren say, T* is simply the name for Zeiss multicoating (T = transparent), begun in 1936 and improved (higher light transmissiion) in the early 1970s. Nothing particularly special (except the early timing of the pre-war invention), as all reputable optics manufacturers for cameras apply their own multi-coating formulae. More important is the quality of lens design, materials used, and production standards. You often pay for what you get. Some exceptions are the truly excellent but economical 21 mm and 28 mm Yashica ML optics for SLRs, and at the other end, some not so excellent but very expensive Leica and Zeiss lenses. In general, the latter names often assure very high quality, and the high prices are justifiable. My standard Planar 50mm f1.4 T* lens worked well on my manual SLRs (139 Quartz, Yashica super 2000), but some MM models were better adapted to the more automatic cameras, like the 167, later.

I don't think the 50/1.4 Zeiss Planar for the Contax SLRs has six elements. I think it has seven elements. It appeared somewhere n the 1975-1976 time frame and I think its formula may have been updated in 1999. Over time most manufacturers switched from six to seven elements for their f/1.4 standard lenses. Konica made the change from 57/1.4 to 50/1.4 (7 elements) in 1973. Minolta went from the 58/1.4 to the 50/1.4 (7 elements) at about the same time. Canon made the change in 1968. Asahi seems to have made the change even before Canon. There are many good manual focus f/1.4 standard lenses. At this point the condition of the lens and the care with which it is used are more important than a lab test from many years ago.