Narrow focus?
First, I'm assuming that when you said
you meant for those to come as issues. If I'm wrong in assuming that, please let me know where or how I can submit them in the future.
Next, I think this is a pretty cool idea for a project, but it seems like it might be a monumental task to gather all the data necessary to make it useful. Additionally, in many cases there may not be even approximate equivalents, or they may have so many differences that someone who finds the equivalent of X in language Y may be very disappointed to find that it's far more different than they felt led to believe.
I think both of these could be (at least partially) solved by starting out with a much narrower focus, perhaps on just the equivalents of various Ruby projects in Crystal.
This would be very useful to Crystal programmers, who are very often coming from a Ruby background, and know how to do something in Ruby but have no idea how to do it in Crystal.
Once sufficient progress is made with Ruby <=> Crystal, then it might make sense to start selectively adding other languages.
I don't mean to be discouraging. If you think you can manage to pull off setting up all the data for a many-to-many relationship between languages, please don't let me stop you. But I think focusing more narrowly might enable the project to build a stronger foundation, and have a better chance at success.
Also, because of the strong relationship between Crystal and Ruby, it seems (to me) very likely that in many cases there will be a strong similarity between Ruby projects and Crystal projects, and in fact many Crystal projects will/are describe themselves as "X in Crystal".