https://github.com/mozilla/common-voice/blob/main/server/data/ar/sentence-collector.txt indeed contains more than 5k sentences, and it has also been enabled for contribution since mid of 2019: https://github.com/mozilla/common-voice/blob/main/locales/contributable.json#L3. Therefore my guess would be that there are no new sentences available for recording, as all the existing sentences have already been recorded. See Single Sentence Record Limit feature release.