Most projects (notably libass) seem to #include fribidi with its path:
#include <fribidi/fribidi.h>

The pkg-config file generated from fribidi.pc.in, on the other hand includes the fribidi subdirectory in the cflags:
Cflags: -I${includedir}/@PACKAGE@


This means that projects using include statements relative to PREFIX/include fail to build when fribidi is not installed in a common prefix.

Could you please change the .pc file, so that the "normal" way of writing include-statements works with fribidi?

->
Cflags: -I${includedir}/@PACKAGE@ -I${includedir}