missing glyphs on web pages
Android keeps track of fallback fonts via a file at /etc/fallback_fonts.xml. After adding your fonts to /system/fonts, you can add a new family node to the XML file like this.

&lt;familyset&gt;
    &lt;family&gt;
        &lt;fileset&gt;
            &lt;file&gt;Custom-Font.ttf&lt;/file&gt;
            &lt;file&gt;Another-Custom-Font.ttf&lt;/file&gt;
        &lt;/fileset&gt;
    &lt;/family&gt;
[rest of file...]


Make sure to make a backup first, and you might need to reboot for it to take effect completely.