With the PostgreSQL 11 release notes acknowledgments list, FOP reported

WARNING: Glyph "?" (0x144, nacute) not available in font "Times-Roman".
WARNING: Glyph "?" (0x15e, Scedilla) not available in font "Times-Roman".
WARNING: Glyph "?" (0x15f, scedilla) not available in font "Times-Roman".
WARNING: Glyph "?" (0x131, dotlessi) not available in font "Times-Roman".

This is because we have some new contributors whose names use letters
that we haven't used before, and apparently FOP can't handle them out
of the box.

For now, just fix this by "unaccenting" those names.  In the future,
maybe this can be fixed better with a different font configuration.

There is also another warning

WARNING: Glyph "?" (0x3c0, pi) not available in font "Times-Roman".

but that existed in previous releases and is not touched here.