"Y'all" perhaps, but "you all" translates to "te kaikki". I'm aware that "y'all" is just short for "you all", but there's also "all y'all", which is more inclusive. Just "y'all" may refer to a certain set of members within a group (just like "te"), but "all y'all" definitively includes everyone in the group (just like "you all" and "te kaikki"), so as far as I know, there can be a subtle difference in usage between "y'all" and "you all". Either way, "you" means both "sinä" and "te" so it's not necessary to use different words for them.
When it comes to writing English translations, I don't think other courses approach this matter any differently. But when it comes to writing translations in the other language, there may be sentences where something indicates that the plural 2nd person pronoun is the only option. For example in the German course, the learner would be required to translate "you two" as "ihr beide(n)" because "du beide(n)" just wouldn't make sense.