Online collaboration has become a regular practice for many Internet users, reflecting the emergence of new participatory cultures in the virtual world. However, little is yet known about the processes and conditions for online collaboration in informally formed writing spaces and how these create opportunities for participants' identity work. This ethnographic case study explores how four young adults, fans of the show "My Little Pony: Friendship is Magic" (bronies), negotiated a dialogic space for their online collaboration on a fan translation project and how this created opportunities for their identity work. After a year of participant observation, we collected interviews, ethnographic diaries and participants' chats, which were analysed with qualitative content and discourse analysis methods. The findings showed how the Etherpad online writing platform used by the participants facilitated the construction of dialogic space through the visualization of a shared artefact and adjustable features. It was in this dialogic space where the participants negotiated their expert identities which furthered their discussions about writing, translating and technological innovations. The study advances present-day knowledge about online collaboration in affinity groups, engendering the construction of a dialogic space for collaborative writing and participants' identity work.