Babbel show the Brazilian flag on their site for their Portuguese language lessons. Obviously they’re teaching Brazilian Portuguese — so what not actually emphasize that without just relying on a flag (and of course having the added confusion of a Brazilian flag with ‘Portuguese’ underneath).
This blog has discussed the confusion and annoyance that using flags to represent languages can cause. If you look at Babbel’s YouTube channel you can find many examples of this — and specifically in regards to their Portuguese being Brazilian Portuguese.
This really shows the importance of specifying what regional variation of language you’re referring too — and are flags enough to do this? And yet again, are they even appropriate?