In yoga, “bird of paradise” is a deceptively difficult pose.
In Sanskrit this pose is called “Svarga Dwijasana”. Svarga is the word for “heaven” or “paradise”, and “dvij” means “twice born”.
“Twice born” is the name given to people of higher castes in medieval India. Physical birth is the first one. The second birth refers to a spiritual one that takes place when a person undergoes an initiation ceremony, which signifies taking on the responsibilities of one's caste.
So I guess one could say the proper translation of “Svarga Dwijasana” is “pose that gives a heavenly feeling to the person of high caste.”
Since most teachers were Brahmins (highest caste), and all their students were from higher castes too, it is understandable why such a name might be used.
The West is founded on principals of egalitarianism (equality) so the Indian caste system, which divides society into hierarchies, has a strong stigma attached to it. Teachers brining yoga to Europe and the US did not want to get embroiled in the controversies surrounding the caste system.
So one can see how it was easier to pick the word “svarga” (paradise), ignore the word “dvij”, and go with “bird of paradise”. After all, the finished pose does have a remarkable resemblance to the flower known as “bird of paradise”.
On an unrelated note, “heavenly” is definitely not the feeling I get when attempting this challenging asana.
If your body is tight like mine, just wrapping one’s arms behind while reaching under one’s thigh is hard enough. Then we add a wobbly balance on one foot. Finally having a futile argument with my tight hamstrings to allow the top leg to be fully extended usually ends in me (apologies to my yoga teachers) using inappropriate words under by breath whenever I try this pose.
So maybe "bird of paradise" is a better translation anyway.