How to Change default fallback font (for non-latin languages)
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Add it in the Language Preferred Fallback List as you did, but make sure you are using the PostScript name for the font. It has to be exact!
&lt;array&gt;
    &lt;!-- for Thai  --&gt;
    &lt;string&gt;th&lt;/string&gt;
    &lt;!-- below is the case sensitive PostScript name  --&gt;
    &lt;string&gt;CSPraJad&lt;/string&gt;
&lt;/array&gt;

References:
https://gist.github.com/Moligaloo/3180490
https://github.com/zerustech/font-fallbacks-tutorial
https://github.com/zonble/tcfail/