Is something like smart contracts possible in Stellar? And if yes, what programming languages could be used to write them?
There is no Turing complete language that is executed as part of the system like in Ethereum and others. That's one of the reasons transactions are so fast on the Stellar network.
But you can have some sort of smart contracts that are based on multi signatures or future executions. There is an example in Jed's blog.
Yes, there is something similar, but no programming language is needed.
The smart contracts functionality is possible by using operations that allow for offer management, payment, while adjusting time-bounds configuration, more. There are a few examples given in the Stellar Smart Contracts Walkthroughs