。。
She can speak Spanish — let alone English, that goes without saying.
Literal
She [topic-は] Spanish [object-を] can-speak. Let-alone English [contrast-は] needless-to-say.
A two-sentence reasoning chain. The first establishes a baseline ability (Spanish — relatively unusual among Japanese speakers). The second uses ましてや ('let alone, much more so') to argue from greater to lesser: if she can do the harder thing, the easier one follows. 言うまでもない ('it goes without saying' — literally 'no need even to say') seals the argument. English is positioned as the easier case because it's by far the most studied foreign language in Japan, taught from elementary school onward. The は after 英語 is contrastive — setting English apart as the contrasted item.