I live in the UAE where we find almost equal distribution of mosques praying 20 as well as 8 rakaths.
The Imams of the mosques praying 8 rakaths quote the proof from sahih Bukhari wherein
Aysha (RA) says that Rasulullah (PBUH) has never prayed more than 8 rakaths (in Ramadan and otherwise) in the night.
The hadith quoted in support of eight rakats is out of context. It refers to Tahajjud Salaah and not Taraweeh as Hadhrath Ayesha (RA) responded to a query of the practice of Rasulullah (SAW) at night by saying, “Fi Ramadaana Wa Ghairihi” (in Ramadaan and out of Ramadaan) (Tirmidhi).
Taraweeh is confined to Ramadaan and not out of Ramadaan. Therefore, the salaat referred to in the hadith is a perpetual one, which is salaatul Layl (Tahajjud) and certainly not taraweeh. It is ironical that many Middle East countries follow Saudi Arabia in the Hilaal (moon) issue but not in taraweeh where twenty rakaats is performed in both the Harams- Makkah Mukarramah and Medina Manawwarah.
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai