I observed that the people manning the book exchange program
booth at the library (at least Toa Payoh Lib) are young students
who are Chinese (dunno is volunteer helper or paid
part-time)
The book exchange program only allows books of the official 4
languages of Singapore (English, Malay, Tamil, Chinese) as stated
by NLB
English, Malay and Chinese are easy to differentiate
I have doubts whether the young Chinese helpers know how
to differentiate between the many Indian scripts (eg. Malayalam,
Bengali, Kannada, Telugu, Gujarati, Hindi, Oriya) such that they
only accept Tamil books