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.
Mixing code in solutions can get real messy real quickly, its never clear what method you are calling from where, to keep it nice. Develop in separate Solutions, it will keep your projects easier to track and make sure you are not confusing languages inside projects