How does "Streak with Steve" work?

Hello, I am participating in “Streak with Steve”. Until today I thought it is limited to one language (Persian in my case), but is that correct? I changed for my second language (Mandarin) and tried to join the challenge also for this language, but it is not possible, I can only leave the challenge. Would that mean that reaching my target in Mandarin would contribute to the challenge that I started with Persian? I will try what happens, but some enlightment from an experienced colleague would be appreciated. Best greetings grom Germany!