I wouldn't call it unfair, but if you're giving the candidate the option to solve a problem in their language of choice, you may run into this. You can either c

I wouldn't call it unfair, but if you're giving the candidate the option to solve a problem in their language of choice, you may run into this. You can either constrain the problem (we work with languages X, Y Z, so pick either of those) or still give them the option but use it in another way. For example, I work in front-end but I do most interviews across front-end, back-end, devops, always together with someone who's familiar with the domain or the specific stack we're recruiting for. In that case I'm there to test more on softer skills, but also its a good test to see if a candidate can discuss their domain with someone who isn't familiar with it.