Comment 12 for bug 539008

Does this twist for 89-ttf-thai-tlwg-synthetic.conf help for your case?

        <match target="pattern">
                <test name="lang" compare="contains">
                        <string>th</string>
                </test>
                <test qual="any" name="family" compare="eq">
                        <string>MS Sans Serif</string>
                        <string>Microsoft Sans Serif</string>
                </test>
                <edit name="family" mode="append" binding="same">
                        <string>Loma</string>
                </edit>
        </match>