I know Jake DID misread it, but ultimately it shouldn't be misread as START because that row of controls is specifically for that conversation. So to keep it consistent with other parts of XenForo, you would never expect to see a Start Conversation link there. Actions such as that are always at the right hand side of the breadcrumb as a Call to Action button.
It should remain as Star Conversation because that's what it does
It's just one of those things where you won't make everyone happy. The phrase could be changed and another group wouldn't like it, same rule for the icon in that some people like the star, some would like another icon me personally I wouldn't see anything wrong with a Lens flare being thrown in there. I think @Chris Deeming said it nicely - "with great power comes great responsibility". Okay, he never technically said this but this would have been the cherry on his post.
I saw it yesterday in the phrases while translating. I actually first translated it as "add to favorites" (in Dutch) but then I realized Gmail had basically standardized this term "Star" so over time this will probably become more familiar with people in relation to the inbox, if not already.
Also bookmarks or favorites can be confused with the ones of the user's browser, so for that reason actually not the best choice. However the phrases are there for a reason, people can pick whatever they like best.