。
She speaks not only English but also French.
Literal
She [topic-は] English [only-だけ] [is-not-でなく] French [also-も] speaks.
~だけでなく…も is the standard 'not only X but also Y' construction. Built from だけ ('only') + でなく (negative of the copula で), it literally reads 'not stopping at just X.' The follow-up clause then takes も to mark Y as the additional fact. This pattern is everywhere in writing and formal speech where the speaker wants to upgrade an expectation: 値段が安いだけでなく、品質もいい ('not only is the price low, the quality is good too'). The colloquial casual variant is ~だけじゃなく.