Species: Udara dilecta (Moore, 1879)
Common name(s): The Pale Hedge Blue
Photography location: Cuc Phuong N.P. (Ninh Binh Prov.)
I am not sure 100% of this identification. I hesitated a long time between the Plain Hedge Blue Celastrina lavendularis and the Pale Hedge Blue Udara dilecta, and finally chose the latter. Underwings patterns of these 2 species are incredibly similar - although they belong to different genus. A view of the upperwings would have been very helpful to clinch the identification.