> path <- iconv("brûlée.png", to = "UTF-8")
> png(filename = path)
Note that the string 'brûlée' can be represented in the system locale in this case (latin1); I believe the issue is a missing translation from UTF-8 to the system encoding when generating the file. Note that 'brÃ»lÃ©e' is the correct byte-sequence for the above UTF-8 encoded string; those bytes are simply being mis-interpreted in the system encoding.
Perhaps there's a missing 'translateChar()' call somewhere?
R Under development (unstable) (2016-11-13 r71655)
Platform: i386-w64-mingw32/i386 (32-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1
 LC_COLLATE=English_United States.1252
 LC_CTYPE=English_United States.1252
 LC_MONETARY=English_United States.1252
 LC_TIME=English_United States.1252
attached base packages:
 stats graphics grDevices utils datasets methods base
loaded via a namespace (and not attached):