JUCE’s centering algorithm does not use that function, though, so the centering issue demonstrated here is still present.
But @migizo pointed in the right direction (thanks!). The following modification to juce_GlyphArrangment.cpp (line 482) could be a fix for the issue:
if (justification.testFlags (Justification::horizontallyCentred))
{
auto font = glyphs.getLast().font;
auto kerningOfLastGlyph = font.getExtraKerningFactor() * font.getHeight() * font.getHorizontalScale();
moveRangeOfGlyphs (startIndex, num, deltaX + kerningOfLastGlyph * 0.5f, deltaY);
}
else
{
moveRangeOfGlyphs (startIndex, num, deltaX, deltaY);
}