。
My sister is fluent in English and French.
Literal
Younger-sister [topic-は] English-French [object-を] use-masterfully.
英仏語 abbreviates 英語 (English) and フランス語 (French) into a compact compound using 仏 (ぶつ/ふつ, the kanji abbreviation for France). 使いこなす ('to use masterfully, to handle with ease') is a compound verb — 使う ('use') + こなす ('manage/handle').