The Planetary Society

Here I have discovered a site that claims to be putting together a disk of multimedia, which they will then send to Mars. This will be a kind of time capsule, the intention being for a future Martian, decedent of the first colonizers from Earth, to pick up this disk and figure out how to play it. Thereby, the members of the Planetary Society can say 1) that they existed, and 2) give the Martians a glimpse of the place of their planet in the course of human history.
Now, this sounds rather slick, and is a good stab at a piece of immortality for anyone who wants to include their name on the multimedia disk (which anyone is welcome to do). Should it actually work as planned, it would certainly be interesting, since views of history do change a good deal according to politics and the state of the world. No matter what young Martians will eventually learn about their planet and the blue-green star their ancestors came from, a time capsule from the Planetary Society would give them a very different perspective on that star, and themselves. Imagine if we uncovered such a thing, a message from people who considered us aliens, wishing us well.
A few of the problems with this scheme that I foresee:
1) Can we really expect that such a time capsule survives for as long as they think it will?
2) Especially if, as the website suggests is possible, Mars is Terra-formed and given a new atmosphere which contains oxygen? (They paint this idyllic picture of their disk just sitting out on a green Martian field, and a young Martian just strolling up and thinking, "By Jove. A relic." And picking it up.)
3) Most importantly: even if they get this disk to work for them, how likely is it that Martians of many generations in the future could understand our language?
If I had to bet, I would put all my money on English being the common Martian language once Mars does begin to be settled by permanent residents. English is truly the international language of today. More importantly, at this point the US is the most likely nation to go to Mars first, though it is more than conceivable that this could change. Martian colonists might start out by speaking Chinese. Yet no matter what they start with, after a few generations the language will have changed a bit. Perhaps more than a bit. Eventually, it is possible that interpreters will be required to translate between Martian and English.
If we reach a point where Mars is colonized, or further still, if it is an independent planet, I imagine that technology will be such that Earth will be very "small" and interconnected, in terms of communication and distance: even more so than today. It might even essentially be one entity, rather than a multitude of nations (not sure if I like the idea). In any case, the easier it is to talk and travel around the globe, the more languages we tend to lose. I hope many, many Earth languages other than English survive such an interconnected future age.
I think, though, that on Mars there will probably be only one language. Maybe not if two or more nations establish colonies and do not communicate (ie, US colony and Chinies colony). But it is a much smaller planet, and it will posses from the beginning the technology to speak across its globe. If there becomes a need for residents of Mars to work together and talk to each other, people will become bilingual, and/or one language will develop.
I also think, however, that there will be strong dialects in Martian. It might be rather like Japan: a somewhat compartmentalized society. There will be enough communication between colonies at first so that the language will remain common, but travel from one point on Mars to another will be difficult, given the harsh conditions. So until the planet is Terra-formed or transport becomes easy, colonies will be allowed to develop somewhat independently, and that will make for different Martian dialects.

Or I could be dead wrong.