it´s little bit out of topic. But My experience with mixing dev stack is bad. I think the best approch is keep code clean. If you want use another language you could use microservice architecture or try to solve problem different way.
And I am not sure If this forum best for this type of question ( .net core & PHP Development ). It´s quite general and it depend on use case where you want to use it. Try to ask on stackoverflow.
May be it will be best if you mention scenario where you want to use it.
I also think that it's better to use clean code.
However, there are tasks that are better solved by another technology.
In my case, it's interesting to partially embed pages Angular.
NopCommerce + Angular - such an example would be very interesting. :-)