The percentage of people aged three or over who can speak Welsh fell between 2011 and 2021 in all local authorities except for Cardiff, the Vale of Glamorgan, Rhondda Cynon Taf and Merthyr Tydfil.
Gostyngodd canran y bobl tair oed neu'n hŷn sy'n gallu siarad Cymraeg rhwng 2011 a 2021 ym mhob awdurdod lleol ar wahân i Gaerdydd, Bro Morgannwg, Rhondda Cynon Taf a Merthyr Tudful.