Seems that your dictionary app can't handle html entities at all.
The last thing you could do is
convert the numerical symbols to characters and expect modern day apps to be able to handle unicode directly.
When I posted the DOCTYPE within a code block, I found that some codes were automatically interpreted. So you'll want a low level parser, that only interprets the
&#xXXXX; parts.
I had expected the lookup in reader to be working, though? Should expect to be better even because the <f>-tags are retained now. But apparently it can handle entity names, but not numbers?