Ho-oh was Mew using Transform. And for those who don't think Lucario is legendary just because he was the star of a movie, imagine this: "The Wishing-Star of Seven Nights - Sandshrew!"
As Latios said, Lucario's official name is Lucario. Since "Lucario" contains characters that can't be written in Japanese, the Japanese have to spell it as "Rukario." If you want to think otherwise, you might as well start calling Mewtwo "Myuutsu" and Deoxys "Deokishisu," because that's how both those names are spelled in Japanese characters.