For the channels you mentionned, the team is not yet formed and we don’t know when it will be.
Once you see the moderator icon appearing in the 3rd tab “subtitling team” for each channel, you can contact the moderator of the language you want to subtitle in (Arabic if Arabic, Portuguese if Portuguese…).
So keep an eye on that tab for the meantime.
While waiting, you can:
Look for a show that has the blue tag “on air”, that is being subtitled and that has a moderator icon in your language. Then, contact the moderator to apply to subtitle this show.
You don’t need to look for channels that have 0 sub in your language to begin, look for shows that are being subtitled.
When you will contact moderators, ask at the same time if they don’t have other shows where you could subtitle.