My sister is bilingual, but because she only lived in the U.K. as a child and teenager, there is vocabulary that is used more commonly in adult conversations th

My sister is bilingual, but because she only lived in the U.K. as a child and teenager, there is vocabulary that is used more commonly in adult conversations that she knows, but has a hard time with. So while she is bilingual by any useful definition, there are common scenarios in which she sounds like a foreigner with "very good English" rather than a native speaker. Our grandfather had the opposite problem. He lived in the U.K. from age 18, and only had the very faintest accent, but in his 60s and beyond would be frequently complimented that his German was "very good for an Englishman"