A single language or multiple languages?

Is the answer a single language or multiple languages?

The argument for multiple languages is that each one may offer different strengths and ways of thinking about computation. The set of ideal languages for children may include those based upon different paradigms of programming as well as different levels of concreteness. Special purpose languages may have a role in such a basket of languages since they may provide superior support for certain classes of problems.

Multiple languages that are too similar is counter productive. The LOGO community has suffered from many incompatible dialects.

Ideally different languages should interoperate together well. In some cases it may even be possible for some languages to emit equivalent code for import into a different language.

If these languages can be tightly integrated then is it best to think of them as a single multi-paradigm, multi-layered language?

One danger of multiple languages is that they can obscure how apparently different things may be fundamentally similar. If, for example, a model of the spread of diseases and a model of the spread of technological innovations are built in the same language then the similarity of these processes should be easier to perceive.