Speed up inkscape startup by overriding the `fontconfig` settings. See comment

fonts.conf.xml

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<!-- /etc/fonts/fonts.conf file to configure system font access -->
<fontconfig>

<!-- Font directory list -->
  <dir>/home/ed8/hpf/resources/fonts</dir>

<!-- Accept deprecated 'mono' alias, replacing it with 'monospace' -->
	<match target="pattern">
		<test qual="any" name="family">
			<string>mono</string>
		</test>
		<edit name="family" mode="assign" binding="same">
			<string>monospace</string>
		</edit>
	</match>

<!-- Accept alternate 'sans serif' spelling, replacing it with 'sans-serif' -->
	<match target="pattern">
		<test qual="any" name="family">
			<string>sans serif</string>
		</test>
		<edit name="family" mode="assign" binding="same">
			<string>sans-serif</string>
		</edit>
	</match>

<!-- Accept deprecated 'sans' alias, replacing it with 'sans-serif' --> <match target="pattern"> <test qual="any" name="family">
			<string>sans</string>
		</test>
		<edit name="family" mode="assign" binding="same">
			<string>sans-serif</string>
		</edit>
	</match>

<!-- Font cache directory list -->
	<cachedir>/var/cache/fontconfig</cachedir>

	<config>
<!--
  These are the default Unicode chars that are expected to be blank
  in fonts.  All other blank chars are assumed to be broken and
  won't appear in the resulting charsets
 -->
		<blank>
			<int>0x0020</int>	<!-- SPACE -->
			<int>0x00A0</int>	<!-- NO-BREAK SPACE -->
			<int>0x00AD</int>	<!-- SOFT HYPHEN -->
			<int>0x034F</int>	<!-- COMBINING GRAPHEME JOINER -->
			<int>0x0600</int>	<!-- ARABIC NUMBER SIGN -->
			<int>0x0601</int>	<!-- ARABIC SIGN SANAH -->
			<int>0x0602</int>	<!-- ARABIC FOOTNOTE MARKER -->
			<int>0x0603</int>	<!-- ARABIC SIGN SAFHA -->
			<int>0x06DD</int>	<!-- ARABIC END OF AYAH -->
			<int>0x070F</int>	<!-- SYRIAC ABBREVIATION MARK -->
			<int>0x115F</int>	<!-- HANGUL CHOSEONG FILLER -->
			<int>0x1160</int>	<!-- HANGUL JUNGSEONG FILLER -->
			<int>0x1680</int>	<!-- OGHAM SPACE MARK -->
			<int>0x17B4</int>	<!-- KHMER VOWEL INHERENT AQ -->
			<int>0x17B5</int>	<!-- KHMER VOWEL INHERENT AA -->
			<int>0x180E</int>	<!-- MONGOLIAN VOWEL SEPARATOR -->
			<int>0x2000</int>	<!-- EN QUAD -->
			<int>0x2001</int>	<!-- EM QUAD -->
			<int>0x2002</int>	<!-- EN SPACE -->
			<int>0x2003</int>	<!-- EM SPACE -->
			<int>0x2004</int>	<!-- THREE-PER-EM SPACE -->
			<int>0x2005</int>	<!-- FOUR-PER-EM SPACE -->
			<int>0x2006</int>	<!-- SIX-PER-EM SPACE -->
			<int>0x2007</int>	<!-- FIGURE SPACE -->
			<int>0x2008</int>	<!-- PUNCTUATION SPACE -->
			<int>0x2009</int>	<!-- THIN SPACE -->
			<int>0x200A</int>	<!-- HAIR SPACE -->
			<int>0x200B</int>	<!-- ZERO WIDTH SPACE -->
			<int>0x200C</int>	<!-- ZERO WIDTH NON-JOINER -->
			<int>0x200D</int>	<!-- ZERO WIDTH JOINER -->
			<int>0x200E</int>	<!-- LEFT-TO-RIGHT MARK -->
			<int>0x200F</int>	<!-- RIGHT-TO-LEFT MARK -->
			<int>0x2028</int>	<!-- LINE SEPARATOR -->
			<int>0x2029</int>	<!-- PARAGRAPH SEPARATOR -->
			<int>0x202A</int>	<!-- LEFT-TO-RIGHT EMBEDDING -->
			<int>0x202B</int>	<!-- RIGHT-TO-LEFT EMBEDDING -->
			<int>0x202C</int>	<!-- POP DIRECTIONAL FORMATTING -->
			<int>0x202D</int>	<!-- LEFT-TO-RIGHT OVERRIDE -->
			<int>0x202E</int>	<!-- RIGHT-TO-LEFT OVERRIDE -->
			<int>0x202F</int>	<!-- NARROW NO-BREAK SPACE -->
			<int>0x205F</int>	<!-- MEDIUM MATHEMATICAL SPACE -->
			<int>0x2060</int>	<!-- WORD JOINER -->
			<int>0x2061</int>	<!-- FUNCTION APPLICATION -->
			<int>0x2062</int>	<!-- INVISIBLE TIMES -->
			<int>0x2063</int>	<!-- INVISIBLE SEPARATOR -->
			<int>0x206A</int>	<!-- INHIBIT SYMMETRIC SWAPPING -->
			<int>0x206B</int>	<!-- ACTIVATE SYMMETRIC SWAPPING -->
			<int>0x206C</int>	<!-- INHIBIT ARABIC FORM SHAPING -->
			<int>0x206D</int>	<!-- ACTIVATE ARABIC FORM SHAPING -->
			<int>0x206E</int>	<!-- NATIONAL DIGIT SHAPES -->
			<int>0x206F</int>	<!-- NOMINAL DIGIT SHAPES -->
			<int>0x2800</int>	<!-- BRAILLE PATTERN BLANK -->
			<int>0x3000</int>	<!-- IDEOGRAPHIC SPACE -->
			<int>0x3164</int>	<!-- HANGUL FILLER -->
			<int>0xFEFF</int>	<!-- ZERO WIDTH NO-BREAK SPACE -->
			<int>0xFFA0</int>	<!-- HALFWIDTH HANGUL FILLER -->
			<int>0xFFF9</int>	<!-- INTERLINEAR ANNOTATION ANCHOR -->
			<int>0xFFFA</int>	<!-- INTERLINEAR ANNOTATION SEPARATOR -->
			<int>0xFFFB</int>	<!-- INTERLINEAR ANNOTATION TERMINATOR -->
		</blank>
<!--
  Rescan configuration every 30 seconds when FcFontSetList is called
 -->
		<rescan>
			<int>30</int>
		</rescan>
	</config>

</fontconfig>

text2font.bash

#!/usr/bin/env bash
# DESCRIPTION
#   Select all text node and create a union of them
#
# USAGE
#   bash ./resources/scripts/svg-text2svg-font.bash
#
# @author: Édouard Lopez <[email protected]>

scriptDir="$(dirname "$0")" # emplacement du script
. "$scriptDir"/envrc # project variables

inputFile="${2:-"$HPF_UNIHAN_READING_SHORT"}"

# env
export XDG_CONFIG_HOME="${HOME}/.config-xvfb-default"
export XDG_CACHE_HOME="${HOME}/.cache-xvfb-default"
# export GTK2_RC_FILES="${XDG_CONFIG_HOME}/gtk-2.0/gtkrc"
export FONTCONFIG_PATH="${HPF_FONT_DIR}"
export FONTCONFIG_FILE="${HPF_FONT_DIR}/fonts.conf"

# Fake a X server
Xvfb :8 -screen 0 1024x768x8 &> /dev/null &
XVFB_PID=$!
echo $XVFB_PID > ./xvfb.pid
export DISPLAY=":8"

printf "Removing existing SVG-font files…\n"
rm "$HPF_SVGFONT_DIR"/*.svg

inkscapeOptions=(
  --select=canvas --select=hanzi --verb=AlignHorizontalLeft --verb=EditDeselect
  --select=canvas --select=pinyin --verb=AlignHorizontalRight --verb=EditDeselect
  --select=canvas --verb=EditDelete --select=hanzi --select=pinyin
  --verb=AlignVerticalCenter --verb=SelectionUnion --verb=FileSave --verb=FileQuit
)

for f in "$HPF_SVGTEXT_DIR"/*.svg;
do
  nf="$HPF_SVGFONT_DIR/${f##*/}"
  cp "$f" "$nf" ;

  printf "creating SVG-font: %s\n" "$nf"
  inkscape -f "$nf" "${inkscapeOptions[@]}"
done

kill $XVFB_PID

I created a light font config that declare a <dir> to only one directory that contains exactly what I need for my script. This help reduce the processing time by 50%.