Sorry for kinda necro-bumping this thread, but it was the first result on Google, so I thought I’d share my findings here.
First, the broken unicode char seems to be because of a buffer overflow in hddtemp, and a bug has already been submitted to RedHat YEARS ago. However, it seems they only fixed it for their own distribution.
It seems that the software didn’t receive any updates in years anyway, the GitHub is pretty dead, and on GNU Savannah it’s marked as orphaned.
So, I guess the best idea would be to switch over to a command line based sensor parsing the outputs from smartctl…