IMO, a large part of being a successful programmer is to know how / with what patterns to approach the problem at hand (in your case: the goal set by the client

IMO, a large part of being a successful programmer is to know how / with what patterns to approach the problem at hand (in your case: the goal set by the client). the actual language most the time is just the means and quickly learned. that said, when it comes to actual code quality, experience is important too: each language or framework has its irks and special feature. i have taken on freelancing work in languages and/or frameworks unfamiliar to me, but spent 1-2 weeks beforehand learning the basic stuff on my own time. if you feel unsure whether to take on the job or not it's probably best to be honest to the customer - let them know that it is your first project with language x or framework y, but that you'll be willing to invest in it and provide them with a good solution. and last but not least there's the saying "learning by doing" :)