File path with UTF-8 characters not found

When I use such a filename, this happens:

$ pdftk modules/custom/fillpdf/tests/modules/fillpdf_test/files/fillpdf_Ŧäßð_v3â.pdf dump_data_fields_utf8
Error: Unable to find file.
Error: Failed to open PDF file:
   modules/custom/fillpdf/tests/modules/fillpdf_test/files/fillpdf_????????_v3??.pdf
Done.  Input errors, so no output created.

If I instead cat the file and pipe that to pdftk - dump_data_fields_utf8, it works fine. That's why I think there might be something internal to pdftk-java happening.

My locale looks like:

$ locale
LANG=en_US.UTF-8
LANGUAGE=
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

I believe that the locale should be detected properly. Is it possible that I was missing some dependency during the build or something? I'm running a built 3.0.9 native image.