Right now GWeather does:

  g_snprintf(buf, sizeof (buf), _("%d \342\204\211"), (int)floor(far + 0.5));

(4 instances, 2 for each of degrees-C and degrees-F)

The problem is that these characters are rare and and don't appear
in many fonts, so you'll get random fallbacks to whatever has the character
on the system.

It would be better to use the degrees-character + a C or an F. If a font
wants to improve the kerning on that pair or the placement of the degrees
sign, we have the technology to do it properly in the GNOME desktop.

Unfortunately these strings are in the .po files. I think the right thing
to do is to do a search-and-replace across the PO files for the degrees-C
and degrees-F characters and replace them there. There are almost no real
translations for these (just he and ar for fahrenheit, for example) and
the translations that are there a affected properly by that replacement.