I think this can be clarified a bit more, I've talked with many BNs and mappers about this change and almost every single one thought the "This is to enable users to search using these terms in-game like they do on the website." part meant that you should just put the genre of the song (things like dubstep, psytrance, actual genres, etc.) in the tags so people can search them. When informed that this actually meant to put the site-specific "genres" (that aren't actually very useful outside of electronic, anime, rock and pop. What the hell is the difference between novelty and other?) they immediately said I was just wrong (I'm not... right?) and that it meant to just put the actual genre of the music and not the arbitrary site-specific "genres."
This lack of immediate understanding of the guideline will lead to unnecessary arguments (as if there haven't been already) and general confusion among mappers, and evidently, BNs. I would propose that something is added to the guideline to make it more obvious that the genre tag is not the actual genre of the map, but instead the site-specific genre tags. I don't know how to word something like that, though, considering a lot of people don't even know that the beatmap search page has an extended genre and language and whatever else search function.
Apart from the clarification, something completely separate: Wouldn't it just be easier to make the in-game search similar to the on-site search? Something like genre=electronic lang=french? As far as I know, only standard has an issue with putting the genre and language on maps, but it honestly doesn't seem like a good excuse to put a whole ass change in the RC considering it takes like 30 seconds to determine a map's genre and language. Also, who is asking to be able to search in-game like they search on-site? Seems to me like we're trying to fix a problem that never existed.
Oh and one more thing, "Exceptions would be when language and/or genre are not clear" why does this exist for the genre when we literally have an "other" genre (and "novelty" but, again, what is the difference)? Should probably be rephrased to something like "The 'other' tag can be used for songs that do not fit in a site-specific genre. Exceptions would be when language is not clear." As far as I know, we use "other" for exactly this purpose already so the guideline should follow.