I work for a mobile startup where, for historical reasons, our chosen language was C#. I was recently assigned to a small project to build a tool that would be used by us internally. When I explained my intention to use Python to build this tool I was heavily criticized for this because introducing new languages, and technologies (Debian, Apache, Python and Django) into our ecosystem would make it harder for other developers to maintain (because only two other people know more than one language besides C#). I countered that this project would take far longer to develop in C# (which I think is an inherent problem with the language/.NET framework) and that the project was small and designed to solve a very particular problem. Of course it is necessary that the ecosystem be as a homogeneous as possible but if your are developing tooling, infrastructure, and internal systems when there are better things to build them with than C# then you should consider using them. By using one language you exclude a lot of other great libraries and frameworks out there, and this case it was the difference between taking one week to build in Python as opposed to a month in C#. Do you think it is acceptable to understand and use only only one language at a startup or even a larger company? Am I perhaps being naive??