Long-tailed Blue Butterfly / Pea Blue Lampides boeticus

Long-tailed Blue butterfly
faded Long-tailed Blue
The Long-tailed Blue butterfly can be distinguished from Lang's Short-tailed Blue by the broad white streak near the border of the underside wings.
The Long-tailed Blue above left still has its long tails and "eye-spots" but the faded one above right has lost its long tail (to a bird or to wear and tear).

Lang's Short-tailed Blue Butterfly Leptotes pirithous

Lang's Short-tailed Blue butterfly
Lang's short-tailed Blue
Lang's Short-tailed Blue butterfly doesn't have the broad white streak near the border of the underside wings visible in the Long-tailed Blue
and, as its name suggests, has a somewhat shorter "tail".
Pair of Lang's Short-tailed Blue butterflies Pair of Lang's Short-tailed Blue butterflies
Langs
Male Lang's Short-tailed Blue
Male Lang's Blue
Male Lang's butterfly
Lang's male (photos above), a little similar to a dull Common Blue with eyespots and tail from the topside.
Female Lang's Short-tailed Blue
Female Lang's Blue
Female Lang's Blue butterfly
Lang's female (the one in the foreground) with an iridescent blue patch on topside of wings.