Unlike searching for R questions on Stack Overflow itself, chatrooms cannot be filtered by [R]. If you try to filter on "R" you get 26 pages of every room whose name happens to contain the letter 'r', not the word.
It turns out there is in fact a chatroom for R, but I gave up on finding it with Stack Overflow, it can only be found with Google(!): http://chat.stackoverflow.com/rooms/106/r
As per "Assign tags to chat rooms", this is one more solid reason, especially for our brethren who name their languages with single-letters. But I'd call this an outright bug, not an enhancement, since R-language rooms simply cannot be located with the filter.
PS: I guess I should make this into a question. Are there other cases where filter-by-tags is sorely needed?