编辑字体配置文件

$sudo gedit /etc/fonts/conf.avail/69-language-selector-zh-cn.conf

在配置文件的monospace段添加 <string>Droid Sans Mono</string> 并放在第一个位置

例：

	<match target="pattern">
		<test qual="any" name="family">
			<string>monospace</string>
		</test>
        <test name="lang">
            <string>zh-cn</string>
        </test>
		<edit name="family" mode="prepend" binding="strong">
			<string>Droid Sans Mono</string>
			<string>WenQuanYi Zen Hei Mono</string>
			<string>HYSong</string>
			<string>AR PL UMing CN</string>
			<string>AR PL UMing HK</string>
			<string>AR PL New Sung</string>
			<string>AR PL UKai CN</string>
			<string>AR PL ZenKai Uni</string>
		</edit>
	</match>