Disclaimer: I am the webmaster of Flarum en Español, providing localized support and translation of the software to users in Spanish
This kind of websites where enthusiastic users (fans as you call them) are giving localized support to other users, translating the software they use and/or developing extensions are very common in the open source scene and even on the proprietary software world and on very few times this have been an issue.
This kind of resources (or fan behavior as you call it) is far more beneficial for any open source community than the harm you say it can potentially cause. And this is a fact, not a conjecture.
You use lot of conditional verbs: It can, it could... Potentially the world could end tomorrow, potentially Trump could win the American elections, potentially IS could win the WWIII, you could run an open source community... or maybe I could rule the World! (Bad things all of them, if you ask me)
