言わずもがな
needless to say, it goes without saying
Noun + は言わずもがな、… · 言わずもがなだ
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言わずもがな is a classical set phrase meaning "it goes without saying": 英語は言わずもがな、中国語も話せる, "she speaks Chinese, never mind English".
It's often used as Xは言わずもがな、Yも, "not to mention X, Y too", like はもちろん (N2). It can also end a sentence: 彼の実力は言わずもがなだ, "his ability goes without saying".
The ending もがな is a classical wish ("it would be good if…"), so it literally means "it would be better not to say it". It sometimes keeps that meaning, "better left unsaid": 言わずもがなのことを言ってしまった, "I said something I'd have been better off not saying".
In everyday speech, 言うまでもない is more common.
Examples
彼の実力は言わずもがなだ。
His ability goes without saying.
彼女は英語は言わずもがな、中国語も話せる。
She speaks Chinese, never mind English.
東京は言わずもがな、大阪も物価が高い。
Tokyo is expensive, of course, but so is Osaka.
つい、言わずもがなのことを言ってしまった。
I ended up saying something I'd have been better off not saying.
結果は言わずもがな、大成功だった。
The result, needless to say, was a huge success.