Hmmm... I don't think official_name applies unless it is really reflected in an official source such as SSO or URA maps?
alt_name could be an option or simply put it as malay name variant, though it may not reflect the reality on the ground.

By the way, it seems like it's now been channeled: 

https://commons.wikimedia.org/wiki/File:Canal_downstream_of_former_Tagore_Stream_towards_houses_on_Lentor_Street,_Singapore_-_2021-12-13.jpg

https://commons.wikimedia.org/wiki/File:Canal_downstream_of_former_Tagore_Stream_behind_houses_on_Lentor_Street,_Singapore_-_2021-12-13.jpg