A language with only a single, open-source implementation controlled by a single vendor, like Go or Erlang, has slightly more risk, in that the single vendor could choose to take the language in a direction you don't like. However, even if that were to happen, it's open source, and the community can maintain it as long as there are enough users.

A language primarily controlled by a single entity that is actively hostile towards openness, like Java, is a little more risky yet, but even so, with enough users it becomes safe enough.

A language that's not open at all, like Mathematica or F#, puts you entirely at the mercy of the company that controls it... but if that company is big and has a good track record, it's still at least a reasonable trade-off.

Now, if something is created by a startup that has at best even odds of being around in five years... you still might take that risk if the technology was open, and you could run it yourself when they close up shop, like, say, Meteor or MongoDB. These are decisions that one is rather more likely to regret, but it's not hard to see how people make them.

However, if a new company introduces a new language that is also it's own walled-garden deployment environment, which you can't run on your own systems, which has no demonstrated history of doing anything well, and which is not open source, anyone choosing that language for a project that's expected to be around for a while would have to be either inexperienced or just plain crazy.