@Miriam That is a whole other question on where to draw the line between fluency, a frequently asked question.
However when it comes to determining "variants" of languages, in my opinion people should be as neutral and objective as possible without taking in any political consideration, especially on a place like Italki and other international language sites.
If you showed a non-native speaker (ie random person) clips of spoken Croatian and Serbian, saying the same sentences, from their neutral viewpoint they would say both are the same language and they couldn't tell the difference because there is no difference. In this case written form is different (as is the case with Urdu and Hindi - Hindustani), but the core of the language is in its spoken form. You can use the term "Variants" for these cases, since they are one language but written in two separate scripts. Back to the example of Farsi, the Dari
"language" (according to Afghanistan) is no "variant" because it's written in Arabic script, the same as Farsi, so there are no excuses for this one.
I would like all these languages websites to adopt new labels and classification based on objectivity. "Variants" can exist when one language is written differently in two separate countries (ex. Croatian and Serbian), but for the ones which have no script difference (Farsi and "Dari", Romanian and "Moldovan", Bulgarian and "Macedonian") they should be under the same label.