It's similar, but not the exact same question. Fluency isn't as good as native, it means you can speak, write and understand the language quickly and efficiently. That is, you can do it without (significant) breaks and errors.
Unfortunately, that distinction is itself quite vague, so putting an exact value on it in SR is hard. My opinion would be 8 dice worth; enough to buy 2 hits (IE you can reliably communicate relatively complex thoughts).