Arabic and chinese each have literary traditions approximately as broad and deep as the western canon. I'm sure there are plenty of others. In all likelihood most excellent and interesting works are not available in english.
Same with the Hindu mythology. As rich or even richer in terms of metaphors and knowledge that can transfer over to modern life.
I have the same thoughts about content on the web
The Russian web is surprisingly helpful for cyber security or undocumented Windows APIs. They also seem to have a better ecosystem of small Windows utilities to do obscure system tasks (like look up your connected USB devices, or check your memory for defects).
also a lot of interesting electronics content in russian
Seems like AI translation is will soon be good enough to explore this. Unfortunately, I think bigger barrier is culture than language and maybe we're not missing out that much in practical terms then.