You may want to ask enough questions of the recruiter who put you forward to discern what exactly the team works on, in terms of languages, architecture, and products, then weight your preparation accordingly. It's really important to not try to go for an amorphous blob of an interview scope, but a very well defined one. Of course, it depends on how technical your recruiter is, which is not much, usually, so when you have the interview arranged you may want to send questions in writing via the recruiter, so that they are answered precisely and by the recruiting person themselves. I wouldn't say that this is a bad idea, because it shows interest and the recruiting manager psychologically invests in you by contributing their time. For quant dev you're looking at only 10% product knowledge, the rest is algorithms. Sorting is nearly always asked. You may want to make sure you have the key numerical methods down to a tee, that you know your memory management and arrays, passing by value and by ref, that you can create a class structure to solve a problem that can also be done using simple functions. Standard issues about polymorphism, inheritance, encapsulation etc should also be covered. I reiterate that it's very important that you know how to design classes instead of just simple functions and that you can quickly handwrite code that solves basic numerical problems.Some other aspects are language specific. I'd say pick the one you're best at, and focus on applications for that alone. Recruiters like to see a strong and cogent story, rather than trying to be a jack of all trades. For proxy measures of demand for skill sets, go to indeed.com and search for each language. The number of search results will tell you what you should focus on.