How does learning a new way to think about a problem become counterproductive? Each language you learn gives you a new angle from which you can approach a problem. Is it counter productive to learn a second spoken language? I haven’t come across an argument against that, even learning a dead language like Latin or Ancient Greek has benefits.
Perhaps counterproductive is too strong a word, but there could definitely be problems in the short term. Programmers love to apply things they learned in their work, and taking a concept or pattern from language A and applying them to language B is a natural reaction. The most common culprits are monads and actors. Ergonomics (readability, cognitive cost, debugging, IDE support, etc) became afterthoughts in the midst of excitement, and the long term health of the codebase (and teammates) suffers.
I have made mistakes like that (introducing monads/future and making the team learn guava) and I still regret it. Its not to say futures are useless - there were a lot of async logic in the codebase and futures solve a real problem, but its not clear if the benefits outweigh the cost.
