The problem is that English speakers might not understand that “Tateyama” means “Mt Tate” and Japanese speakers might not understand that “Mt Tate” means “Tateyama”, so Mt Tateyama is a compromise.
I just looked on Wikipedia and see there are two Arakawas (at least); one is the Arakawa River and one is the Ara River.
Wow, this is the most unprofessional copy I’ve seen on Wikipedia! Maybe someone meant to write this on the talk page and accidentally posted in the article? I guess it’s so small potatoes, there’s no editor watching closely.
Anyway, from a Japanese perspective “gawa” isn’t really different. It’s just a voiced consonant shift to better flow with the preceding sound. There’s a word for it, but can’t remember it off the top of my head.
Also, I see that Mt. Tateyama is specifically listed here with "yama." So the article was correct.
I particularly like "Torpenhow"
Mt Matterhorn. Mt Denali. Mt Mont Blanc. Eurgh.
On that note, the <town>, <country> notation is hideous. Paris, France. Rome, Italy.
Bleurgh.