if u don;t speak, don't share your ideas, u gonna do all the worse part of the work, and maybe, if u don;t contribute, the group can kick u out, or give u an 0 for peer evaluation, which will affect your assignment mark.
not much if u still in the group, if u got kicked out, which means you will get 0 for your assignments, and it will affect a lot. See, the groups are all assigned, so u can't blam anyone for that and now is a great chance to start practice your English, we all went through this situation. good luck