You actually allude to the answer in your question.<p>When you say that "as a programmer I should be comfortable adapting to different languages" you expose the key concept that will help you to make the decision.<p>You should do what you're comfortable with.<p>In theory, you're in this field because it's what you love to do. You enjoy it, and we're usually comfortable with doing things that we enjoy.<p>It follows, then, that you should progress when and only when you feel comfortable with making that progression. If you don't feel comfortable and confident in telling your clients that you'll do WordPress work for them, you should not tell them that.<p>Do what you're comfortable with. It's guaranteed to be better for both parties in the end, because you don't end up working on something you don't want to or aren't able to do, and your client doesn't end up with something that is built by someone not confident with the technology they used.<p>However, doing what you're comfortable with comes with one important caveat. You should never be too comfortable with what you're doing... that's a sign of stagnation, something which is sure to be deadly to your career.<p>In your role as a freelancer, it's not your job to accept a position which you're uncomfortable with. However, it is your job as a freelancer to keep learning, to stave off that stagnation.<p>Keep improving your skillset. Always be learning. Be comfortable, but don't stagnate.