My coworker loves X programming language. They have privately worked on some projects with X language, and at every opportunity they will mention than some new project could be written in X language.
The company I work for has a well-defined stack that they have been using for at least half a decade. I'm working in a small tech team with mostly juniors to the tech industry, and I'm also a junior myself. I have my concerns about pushing X language for a couple of reasons:
Our tech team is largely young and inexperienced. We have some members of the team that are still learning about and struggling with the company's stack. I feel like an additional language is going to dilute their efforts.
The coworker pushing for X language is the only one in the team actually fluent in X language. That means that the rest of the team can't fully understand the code the way they do.
The coworker is also pushing side projects related to work in X language. This means that we have to actively review pull requests in a language that we don't fully understand.
This is probably a classic career question, but googling "coworker pushing favorite language" isn't getting me to the results I'm looking for.