What on earth is a "true programmer"? Someone who programs using the one true language using the one true methodology on the one true OS? There ain't no such animal!

It is true that you are likely to learn a greater range of techniques by using a range of languages, but there are people who can write FORTRAN in any language. That doesn't make them more or less programmers, but it may make them more or less good.

One thing that you do learn from using different languages (if you are paying attention anyway) is that they have different strengths and weaknesses and that there is no one language that you would wish to use for all tasks.

In like fashion to languages, different programmers have different strengths and weaknesses and are suited for different tasks. I've programmed in a bunch of different languages (see my home node) and I know that the more languages you have dabbled in the easier it is to pick up another (same's true for natural languages BTW). So get out there and learn as many languages as you can, can't be anything but good for you.