Chamilo lcms connect 2 has been in production in several institutions for the last year or so and will be used in more institutions in the coming academic year, so it can be considered stable. Some parts of the system have been in production in our university for 2 years (so from before the 2.* was actually released)
Chamilo lcms 'connect' 3 has recently gone in production in some institutions too. A 3.1 release is to be expected very soon.
I don't think the 2.1 is available in french. There will be no migration possible between 2.* and 3.*, for chamilo lcms 'connect' 4, the next release to be expected next summer, there will be more update-possibilities as the packet manager will have more functionality by then and update-scripts will be available.
the 'classic' chamilo lms 1.* is a different product. The lcms 'connect' branch was developed because some of the institutions using Dokeos 1.* (from wich chamilo lms 1.* is a fork) didn't think it provided the necessary flexibility to develop new features and re-use objects and also because the code was considered very dated. the classic branch has a much bigger user-base so many people have tries stuff out for you.
You should probably try both versions and see which one suits you the best (feature-wise).
As a developer I strongly prefer the chamilo lcms 'connect' system over the "classic" chamilo lms system. It is however much less documented and you will probably need to do a lot more searching and trying out stuff when you use 'connect'. You definitely need the "pioneer spirit" if you want to go live with chamilo 'connect' and you will need to figure out a lot of stuff for yourself. It is up to you to decide if you want to do that or not. If the 'classic' lms has all the features you want and you are not planning on developing your own applications on the framework, you will probably avoid a lot of frustration by not choosing 'connect'