[samatman]

A language with one implementation can't really be said to have a specification.

It may have a very detailed accompanying technical documentation of what the implementation is supposed to do, this may be called a specification, but a specification deserves the name with a minimum of two implementations.

[FrankHB]

This is technically incorrect. A programming language can be designed with specification in mind, even with a formal one (e.g. SML). It is just true that the specification is not likely effectively verified before more than one real implementations landed, if it is not formally verified. (Anyway, verification by testing of existing implementations _is_ the fallback where people cannot afford the cost of formal methods.)