もし、言う人は「いうまでもない。。。」と言ったら、英語の一番適当な通訳は多分:"Needless to say...", or, "I say (state) the obvious when I say..." etc. 又は "Of course..."
例:「ヨン様の名声は日本にいるのが高いはいうまでもないです」(多分私の日本語は変かも) Ex. "It doesn't need to be said that Yon-sama has a high reputation (or is very famous) in Japan," or, "Needless to say, Yon-sama's fame in Japan is quite high," etc.
ちょっと違うニュアンスが: 例:「彼は2歳で、漢字を分らないというまでもなく平仮名さえ分らないよ」 Ex. "He's 2 years old. Not only can he not understand Kanji but he can't understand Hiragana!"
Variatim: We do use it, but it sounds a bit formal. We often say, "much less" instead of "still less" though. It's more likely we would say, "He can't even understand hiragana, never mind Kanji!" or something like that. Thanks for the help!