> And these things can be enforced by style checkers
At which point you've got a subset of the primary language, and might (if it were available and appropriate) as well be using a language that already had these good style things as language features.
The costs are more around build process and compile time. Whereas the costs for wholesale language migration include the risk of not being able to ship or hire.
knocte, in case you were wondering why you got downvoted (though by the time you read this you may be back to 1 or higher, who knows), on this forum there's a bit of pressure to avoid the "this" and "+1" comments. Some with high enough karma will downvote these sorts of comments when they come across them. To avoid those downvotes, but still post something, minimally add a sentence or two explaining why you're in agreement. For example:
This. With Ada, for instance, there's SPARK which is a restricted version of Ada with additional constructs (in Ada comments) for formally verifying the program. Spark, then, has grown to the point where it's almost its own language (though Ada compilers can handle it because of how the annotations are placed in comments).
At which point you've got a subset of the primary language, and might (if it were available and appropriate) as well be using a language that already had these good style things as language features.