Thank you very much for picking this up!!
I know a few of the fandom terms in the untranslated page, so here's a rough definition for those who are curious:
オフ会 (offkai): Offline meeting.
オンリー (only): A doujinshi event limited only to a work, ship, or character. For example, "Genshin Impact Only" means a doujinshi event only for Genshin Impact.
カップリング (coupling): A romantic ship, usually abbreviated as CP.
サークル: Circle, a group for creating doujin works.
地雷 (jirai): Literally means landmine, something you dislike/hate in fandom (like NOTP or a trope you dislike).
死ネタ: A work where a character dies.
同人誌 (doujinshi): A self-published book.
同担拒否 (doutan kyohi): Also abbreviated as dtkh sometimes, someone who dislikes sharing their favorite(s) with someone else, and refuses to interact with people who has the same favorite(s). Also used as a warning for people with the same favorite(s) to not interact. Uni is this.
二次創作 (nijisousaku): Derivative work, basically fan work of an existing IP.
夢小説 (yume shousetsu): Literally "dream novel", a story where fictional characters interact with readers/self-insert, but nowadays can also be OCs.