I've interviewed at a company that uses their own in-house programming language; I don't think any others use it. They have not mentioned using any other languages or what they use for a development environment. I just graduated from college with a degree in CS, so I would like to find a job where I can learn more about the field and build up some professional experience. This question might apply to programmers with more experience too.

What are the pros and cons of taking a job like this? If I were to switch jobs later, would I have to start looking for entry level positions again because I haven't gained any language-specific experience?