@Marinetta
Oh I see, very interesting! Thanks.
@Parker231
"I class fluent as being able to read, write and speak the language at the same level as your birth language."
Hmmm, i would define it differently. It is very difficult to speak another language to the same level as your "birth" language (side note - what is birth language, is it the mother's language or dominant language in country of birth?). If someone does, I would call then bilingual/multilingual.
I think "fluent" is a lower level of proficiency but it still means that someone is able to communicate effectively (orally and in writing) in various contexts - everyday, social, professional. To achieve that you do need to have lived in the country or at least visited regularly and/or for prolonged periods - or speak the language with a parent.
I am fluent in French (I've studied it, lived there, speak it daily with DH and visit France regularly) but I absolutely do not speak it to the same level as I speak English.
We are hoping to raise our son bilingual ie speaking both languages to the same level, but there's a lot to consider to give him the best chance of achieving that.