(P.S.: Do you mean Flemish or Dutch? - Flemish is more of a Dutch dialect really, but ... I've always made the distinction in order to not appear rude to Belgians)
I don't know really. The cycling events I'm watching are being held in Belgium, and I
know the commentary is not in French, so I suppose I
assumed it was in Flemish (in some cases the video I'm watching says so), but I don't know if I would be able actually to distinguish between Flemish and Dutch.
I've often heard it said that a language is just a dialect with an army. There's some truth in there.
Certainly the distinction is often more cultural and political than linguistic. It is common, for example, to refer to Cantonese, Shanghainese, Mandarin, Hakka, Hokkien etc. as "dialects" of Chinese, when they are as mutually incomprehensible as English, French, German etc., which are all accorded the status of "languages". There are two reasons for this, I think. One is that
written Chinese is basically the same for all the "dialects", but the other is the deeply-rooted cultural belief that "there is only one China". Ever since the unification of China in 221BCE, and however imperfectly this belief has conformed with reality, Chinese people have believed that China was one nation, and they were all one people, so it followed that they had one language, and that variations were dialects.
However, the languages spoken by some ethnic-minority peoples in China (Russian, Mongolian, Tibetan, Uygur, Kazakh etc.) are called languages, not dialects, reflecting the "ethnic-essentialist" view of Chinese identity held by both most foreigners
and most Chinese people.