works for me.
That is most likely happens if applications links older fontconfig statically/dynamically.

Please update that app to link to the right one or simply disable that config if you don't need it.

I'm running Slackware 14.1 x86_64 that uses fontconfig-2.10.93 and I'm experiencing a similar issue when running the Steam client, this is the output I'm getting;

-----------------------------------

Fontconfig error: "/etc/fonts/conf.d/10-scale-bitmap-fonts.conf", line 70: non-double matrix element
Fontconfig error: "/etc/fonts/conf.d/10-scale-bitmap-fonts.conf", line 70: non-double matrix element
Fontconfig warning: "/etc/fonts/conf.d/10-scale-bitmap-fonts.conf", line 78: saw unknown, expected number

-----------------------------------


This is not an upstream bug?


Here is the contents of the 10-scale-bitmap-fonts.conf;

<?xml version="1.0"?>
<!DOCTYPE fontconfig SYSTEM "fonts.dtd">
<fontconfig>

<match target="font">
  <test name="scalable" compare="eq">
    <bool>false</bool>
  </test>
  <edit name="pixelsizefixupfactor" mode="assign">
    <divide>
      <name target="pattern">pixelsize</name>
      <name target="font"   >pixelsize</name>
    </divide>
  </edit>
</match>
<match target="font">
  <test name="scalable" compare="eq">
    <bool>false</bool>
  </test>
  <edit name="scalingnotneeded" mode="assign">
    <and>
      <less>
        <name>pixelsizefixupfactor</name>
        <double>1.2</double>
      </less>
      <more>
        <name>pixelsizefixupfactor</name>
        <double>0.8</double>
      </more>
    </and>
  </edit>
</match>
<!--
  So far we determined the scale factor.  Now, check and if
  scaling is NOT desirable, just reset the scale factor to 1.0.
  -->
<match target="font">
  <test name="scalable" compare="eq">
    <bool>false</bool>
  </test>
  <test name="pixelsize" target="pattern" compare="less">
    <double>64</double>
  </test>
  <test name="hinting" compare="eq">
    <bool>true</bool>
  </test>
  <test name="scalingnotneeded" compare="eq">
    <bool>true</bool>
  </test>
  <edit name="pixelsizefixupfactor" mode="assign">
    <double>1.0</double>
  </edit>
</match>
<!--
  If we *are* going to scale, go ahead and do it.
  -->
<match target="font">
  <test name="scalable" compare="eq">
    <bool>false</bool>
  </test>
  <test name="pixelsizefixupfactor" compare="not_eq">
    <double>1.0</double>
  </test>
  <edit name="matrix" mode="assign">
    <times>
      <name>matrix</name>
      <matrix>
        <name>pixelsizefixupfactor</name> <double>0</double>
        <double>0</double> <name>pixelsizefixupfactor</name>
       </matrix>
    </times>
  </edit>
  <edit name="size" mode="assign">
    <divide>
      <name>size</name>
      <name>pixelsizefixupfactor</name>
    </divide>
  </edit>
</match>

</fontconfig>

Steam client has own runtime library of fontconfig, which is old and not supporting this feature. even if that error happens, it doesn't affect any functionality on that version. if you mind it, follow up the step at comment#1 as I already mentioned.

At the time of my post I wasn't aware that Steam has an issue with this.


thanks

(In reply to Akira TAGOH from comment #1)
> works for me.
> That is most likely happens if applications links older fontconfig
> statically/dynamically.
> 
> Please update that app to link to the right one or simply disable that
> config if you don't need it.

How exactly can I update the app to link to the right one?

(In reply to Tales from comment #5)
> (In reply to Akira TAGOH from comment #1)
> > works for me.
> > That is most likely happens if applications links older fontconfig
> > statically/dynamically.
> > 
> > Please update that app to link to the right one or simply disable that
> > config if you don't need it.
> 
> How exactly can I update the app to link to the right one?

No ABI changes in fontconfig. simply building the latest fontconfig and replace the library in Steam should works though.

(In reply to Akira TAGOH from comment #6)
> (In reply to Tales from comment #5)
> > (In reply to Akira TAGOH from comment #1)
> > > works for me.
> > > That is most likely happens if applications links older fontconfig
> > > statically/dynamically.
> > > 
> > > Please update that app to link to the right one or simply disable that
> > > config if you don't need it.
> > 
> > How exactly can I update the app to link to the right one?
> 
> No ABI changes in fontconfig. simply building the latest fontconfig and
> replace the library in Steam should works though.

Thank you, Akira, for your patience. I am still not understanding, I am a newbie. : )