A single word for someone who is fluent in only one foreign language?

I know you can say bilingual, trillingual, multilingual. But what if I want to emphasise the number (only one) of foreign language, rather than the total number of languages one can speak?

Someone who is only fluent in one foreign language means that he/she is fluent in two languages. That is, he/she is fluent in his/her mother tongue which he/she has grown up listening and speaking since birth, and the other language can be any (foreign) language spoken within the country he/she comes from or spoken in any other countries. For example, a person born in Sri Lanka listens and speaks the language 'Tamil' since birth. Then,Tamil is his/her mother tongue. If he/she can speak another local language called 'Sinhala', then Sinhala is his/her foreign language, or if he/she can speak the language 'Hindi' which is generally not used in Sri Lanka can also be the foreign language. In summary, who is only fluent in one foreign language which is spoken within the country or any other countries can be called a 'bilingual'.

bilingual

able to speak two languages with the facility of a native speaker

http://www.dictionary.com/browse/bilingual?s=t

There are also trilingual, quadrilingual, and multilingual people.