If your
LANG
environment variable doesn't use UTF-8 (e.g. you're using EUC-JP, Big5, GB18030, ISO-8859-1, or something other than UTF-8), the output from something like
curl wttr.in
may not appear properly in the terminal, but you can usually also just use
curl wttr.in | iconv -f utf-8
to convert from UTF-8 to your system's character set as well. This may cause trouble with the colored output unfortunately, so you'll need to use
curl wttr.in?T | iconv -f utf-8
if the output is wrong because of colors. However, encoding issues like this are separate from having the fonts necessary to display the correct characters.
For the font issue I see in the browser screenshot, you appear to be missing CJK fonts to display Chinese, Japanese, and Korean characters. For that, you can install the
x11-fonts/noto pkg/port (it's actually a "meta-port", meaning it actually installs a group of related packages; the download size is ~830 MiB for all of them, if that matters, and ~1 GiB of storage will be required.) You may need to restart your X server to see the correct characters being rendered. You should also verify the fonts chosen by the browser for displaying such characters; your browser may need to be configured to use the necessary fonts.