As others have said very small, especially for someone not an expert in those languages.
It should be done more for interest and generally broadening your skills to make you a better developer.
If you want to learn a new language to get a different kind of job start by considering what kind of job you want and then learn the most used languages in that bracket.
Like c/c++ for game dev jobs, Objective C/Swift for iPhone development, java/kotlin for android and so on. For more generic dev jobs the answer would be that Java or C# would be a good place to start.
It should be done more for interest and generally broadening your skills to make you a better developer.
If you want to learn a new language to get a different kind of job start by considering what kind of job you want and then learn the most used languages in that bracket.
Like c/c++ for game dev jobs, Objective C/Swift for iPhone development, java/kotlin for android and so on. For more generic dev jobs the answer would be that Java or C# would be a good place to start.