No matter what level of expertise, every developer has their views and opinions when it comes to programming language choices. It's much like a toolbox; you use them based on the specific need to solve a problem or fix something. One of the reasons an interviewer will ask this question is to see what range of tools you have used and which you prefer using. It always helps to start by stating that you have used several languages and have a high confidence level with all of them, but if you had to pick, give them a range and narrow to one of your favorites. Don't be surprised if an interviewer asks why you like that language and what benefit it gives you. If the interview is going well, it wouldn't be a bad idea to talk about some of the strengths and weaknesses of a few that you have used.
As a reference, the top languages likely be Python, Java, JavaScript, C, C#, Ruby, PHP, Swift, and SQL.

"Every software developer has a preferred language, and I'm no different. There are a few that I like and would put on my preferred list. Let me start by giving you a few that I have found very useful in various environments. Perl is probably is among the top for me for several reasons. Compared to Python, it is about three times as fast when reading PASTA files, and it only needs half the storage space to store sequences in memory. Java is another one of my preferred favorites, again for many reasons. Not only is it good for programming algorithms, but it can be used across multiple platforms, including web applications. Lastly, in this group, I need to include C# because it requires less memory for holding strings and less time to read these types of files than most other languages."