。
She speaks English, and on top of that, French as well.
Literal
She [topic-は] English [and-と] additionally French [also-も] speaks.
さらに ('furthermore / on top of that') adds emphatic 'and what's more' to the construction; the placement after と and before フランス語も signals that French is presented as a notable addition rather than just a parallel item. Compare with 英語とフランス語を話す (a flat statement of two languages) or 英語もフランス語も話す ('both, equally'). The さらに~も pattern climbs up — 'A, and what's more, also B' — calling attention to the second item.