。
She can speak Russian.
Literal
[topic-は] Russian [subject-が] can-speak.
話せる is the potential form of 話す ('to speak') — '(can) speak.' Crucially, when a transitive verb shifts into the potential, what would be the direct object (marked with を) typically gets re-marked as the subject of the potential (marked with が): ロシア語を話す → ロシア語が話せる. This が-marking on the would-be object is a defining feature of Japanese potentials. Russian is one of the iconic 'difficult languages' Japanese learners reference, alongside Arabic and Chinese.