While you can set your own font in your terminal or other tools, it will not change the default "Monospace" font that some applications use.

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To change that, edit ~/.fonts.conf Show archive.org snapshot and add settings for the "monospace" family. Here is how it looks on my machine now:

<fontconfig>
  <match target="pattern">
    <test qual="any" name="family">
      <string>monospace</string>
    </test>
    <edit name="family" mode="assign">
      <string>DejaVu Sans Mono</string>
    </edit>
  </match>
</fontconfig>

Fill in "DejaVu Sans Mono" with your preferred font's name.