I was reading [this question](https://stackoverflow.com/q/2903430/1882077) when I noticed a curious comment underneath:

> 
> not sure what the question is: you can use VB.NET and C# projects in one solution (though I wouldn't recommend doing so).
> 
> 
> 

I do this quite a bit, as we have legacy VB.Net code, and new code is written in C#. Is this really not recommended? Why not?
['https://Stackoverflow.com/questions/15706564', 'https://Stackoverflow.com', 'https://Stackoverflow.com/users/969613/']
There is no real reason to avoid this, other than adding complexity from having two languages in one "solution".

Your scenario (working with a legacy product, but adding new features) is a valid reason to have both languages used in a single solution, in my opinion.
Why would you want to do that? If you have legacy code what you want to use, you keep that code in its own components, you don't mix it with the new code. It is not recommended because it does not promote "Clean Code". It can lead you to have a solution that is difficult to read and maintain.