As has been said, language won't survive. Thus, don't use language in the first place, use pictures. I would a bunch of pictures made out of a pair of metals that won't corrode--not plating but images that go all the way through the metal. Once you have enough pictures to explain you can use a more compact coding scheme.
You can never predict what's going to happen to any given time capsule so you make a lot of them. Put them in varied environments, including on the moon. I wouldn't put things in orbit because anything put high enough up to last 50,000 years is going to be awfully hard to detect. Make it big enough to be spotted and you're asking for it to get smashed.