[poppler] How to set custom 'share' directory

[Jeroen Ooms]

I maintain the poppler bindings for R which work on Windows, MacOS and
Linux. However Chineese users on Windows/Mac have reported that
poppler doesn't find the share data files:

  error: Missing language pack for 'Adobe-CNS1' mapping

Where exactly does poppler look for the 'share' directory? Is there an
environment variable or libpoppler API that I can use to specify this
location?

Thank you