Is it on-topic to ask something like:
If so, would it be allowed to link to rule book scans made by fans, or should it only be allowed to link to offical sites (resp. rules published by the game author)?
Yes, you can ask if rules are available online. Yes, you can ask for particular language version of the rules. Both of these questions are answerable, and are a problem that many other people may face.
Even though it is a valid question, it probably isn't a very good one. The answer and solution that other SE members will provide will likely just be a Google search that anyone (including the pending asker) could do themselves.
As for linking to rule book scans, I wouldn't link to non-official rule book scans of the official rule book. Rule books are subject to copyright restrictions, so unless the author/owner had given permission to copy and redistribute rule book scans, then the fans who made the scans are breaking the law (BGG requires permission from the author to upload copyrighted works, so you probably can link to rules posted there.)
