EPUBs with UTF-8 encoded HTMLs don’t seem to show up properly. For example, here’s the UTF-8 source code (notice playing card suit characters):
Here’s how it looks like in Sumatra:
Sorry to say this but in terms of indentation, spacing between bullet list points, UTF-8 support and so on the EPUBs just look much better even in Edge†:
Would simply love to see Sumatra improve in terms of how it displays EPUBs, MOBIs and other eBook formats.
† Edit (Oct 3, 2019): Note that subsequent to the closure of the Books category in the Microsoft Store, the legacy Edge ‘Classic’ version will eventually drop support for EPUBs altogether. The upcoming Edge Chromium version doesn’t support the format anyway.