I'm going to remember that Você is synonymous to the Spanish word Usted, which is a plural form of "you" and Vocês is just the plural form. I was really confused. Having a Spanish background really helps.
Same for me...In the tips-section: "from now on vôces is you all..." and bam, the first time I change my habit in order to respect the tip, "WRONG" :-(
Colloquially it does. But "you all" is not standard English (it belongs to a southern US dialect), so it would not be appropriate to use in grammatical instruction.
To use the 2nd person plural in English one says "you all" so Voces são meninas will translate "you all are girls" which is plural what Duo has is in the singular and is wrong.