I doubt this would be disastrous. For example, to post this message, I'm currently using a "stack" that's written in at least assembly, C, C++, Javascript, and Emacs Lisp. And, it's all written by people who aren't even getting paid to do it.
It seems unlikely that 10 developers in a startup wouldn't be able to maintain code written in a few different languages.
The way you keep a codebase easy to manage is to divide it up into small projects that you can "finish". When was the last time you hacked on glibc? Never? That's how parts of your infrastructure should work: get them right, then forget about them. Using the best language for the job makes this significantly easier.
It seems unlikely that 10 developers in a startup wouldn't be able to maintain code written in a few different languages.
The way you keep a codebase easy to manage is to divide it up into small projects that you can "finish". When was the last time you hacked on glibc? Never? That's how parts of your infrastructure should work: get them right, then forget about them. Using the best language for the job makes this significantly easier.