、。
She's proficient in both Spanish and Italian.
Literal
She [topic-は] Spanish, Italian both [subject-が] is-proficient.
共に ('together with, along with, both') here functions as 'both,' linking two items in a parallel pairing. Note the comma separating the two languages without a particle — bullet-style listing common in writing. スペイン語 and イタリア語 are both built on the same template: katakana country name + 語 ('language'). The な-adjective 堪能 takes the listed languages as its scope of proficiency.