Some time ago when I was designing the approach radar module for the ATC simulator for HCAA, the spec was very clear that the limit had to be placed at 45 degrees. So I took it for granted and I didn't make any research of my own.
But very recently I had a discussion that made me wondering and I couldn't find any online documentation. I found Lnafziger's answer suggesting that
Controllers may issue a heading or a course direct to a fix between the IF and FAF at intercept angles not greater than 30 degrees for both conventional and RNAV instrument approaches
So I guess this is it for FAA airspace. But I would like to know if there are any EASA regulations or ICAO recommendations that impose 45 degrees in Europe.