If you only a language, then there is no problem, as long as you can put to work to do a good job on it. In addition, I want to say is, in fact, all programming languages are common, you just need to transform what your thinking, you will find more than actually learning the language is not a particularly difficult task.
Although I am just a front-end engineer, and for many years only write html add css. js language is the most recent 45-year study. But when I mastered the language js, I found another language is not difficult to learn, for example, I now mastered Python and php, there go the language.
I found that almost all languages are common, critical thinking and your program you have to do the project.
For enterprises, he does not care what language you use, it only cares about you can not finish the job he asked you to do, if you do not ask you to complete his work, even if you'll 10,000 kinds of language enterprises will think that you are not worth a penny for him.
So I think you can go to candidates spare time to master the language of many things, you can slowly learn after work, it does not matter, as long as a project to get started, do a do you will be able to grasp.
The above text is only my personal opinion, if Tell me what you have different points of view are welcome to discuss in the comments area, I will carefully answer each comment.