When to use a new programming language - 2

We discussed using new programming languages in last post This took the view from learning perspective and new projects with no legacy to worry about. However, that is rarely the case in professional settings. One has to worry about existing components

Interoperability, languages do provide foreign function interfaces (FFI) mechanisms for handling data type conversions, allocations across language boundary etc. how good and mature are they ?

Build systems, can be tricky, some languages may have their own build systems tightly integrated with. Can you assimilate it into existing build system?

Ecosystem*, is a key piece, does it offer breadth of supporting packages, or will you have to plan to re-implement some of existing functionality

Package size, is important in general but more so in constrained systems, so knowing the cost of size with new language is going to be important factor.

Tools are pillars for productivity, with single languages it is simpler, but with multiple languages involved can these tools offer support across language boundaries stack-walk, throwing and catching exceptions, back-traces etc.

Skill-set upgrade should be easy, if you need to invest to overcome the learning curve or is skill available externally to hire. This can be an important factor on bootstrapping the new language into products.