This blog is updated daily..
A general description is here.
‘capabilities()’ now reports if ICU is used for collation.
(OS X only.) Package ‘tcltk’ checks if it is linked against the CRAN X11-based Tcl/Tk and if so that the Tcl/Tk component and the X11 libraries are installed. This allows more informative error messages to be given.
‘icuSetCollate()’ allows ‘locale = "default"’ to use the OS locale collation category.
‘configure’ reports on the more important capabilities/options which are not compiled in.