It is believed that the book was compiled later than the time of the conversation and that many of the recorded conversations are spurious.
For a discussion see Questions of King Milinda,¹ vol.i.xxv f.
There is a Singhalese translation to it, which is called the Saddharmādāsaya, written in the eighteenth century by a monk named Sumaṅgala. P.L.C.274.
¹ See also: The Debate of King Milinda (ed.)