Speaking a foreign language

conversational (I speak conversational German but my grammar is awful)

разговорный (язык)

accent (Mary's strong strong accent is impossible to understand)

акцент

fluency (My uncle is fluent in five different languages)

беглость / свободное владение языком

pronunciation (John will find the pronunciation of the word squirrel impossible)

произношение

native speaker (I was taught French by a native speaker from Marseilles)

носитель языка

grammar (Dan's spoken Mandarin is bad

but he needs to improve his grammar)

bilingual (My wife is bilingual; she speaks English and Japanese)

двуязычный / билингв

vocabulary (I bought a dictionary to improve my Spanish vocabulary)

словарный запас / лексика

rusty (Sarah's Portuguese is a bit rusty; she hasn't spoken it in 10 years)

подзабытый / «заржавевший» (о языке)

listening (Watching French TV helps you improve your listening skills)

восприятие на слух / аудирование

speaking (The best way to improve your speaking skills is to talk to native speakers)

разговорная речь / говорение

the language barrier (The language barrier stopped me from talking to them)

языковой барьер

reading (Looking at American websites can help you improve your English reading skills)

чтение

make myself understood (After only a few weeks living in Italy I was able to make myself understood)

изъясняться / быть понятым

writing (I understand some Hebrew but I find the writing impossible)

письменная речь / письмо

speak accurately (Although Pedro has a strong accent he does speak accurately)

говорить грамотно / точно

lingua franca (English arts as a lingua franca for the people at the conference)

лингва франка / язык межэтнического общения

pick up quickly (Living in Cairo I managed to pick up Arabic quickly)

подхватить / быстро выучить на практике

translation (The translation on the contract was full of mistakes)

перевод

have a good ear for languages (I have a good ear for languages)

иметь хороший слух к языкам / способности к языкам