Overview of the issue
If you translate your post taxonomy with Remove categories prefix enabled in Yoast’s category URL settings, visiting the translated category will redirect to the default language or display a 404 error. It may also affect canonical URLs.
Do not to translate the category slug. The untranslated term won’t be visible in the URL anyway when Remove categories prefix is turned on.
For me the workaround does not work. The default language works fine, the translations are broken. I did not translate the category slugs.
The links in the language switcher seem to produce the right links to the corresponding URLs, but I get 404 errors on all category archives, except for the default language.
I have the languages mapped to different domains and subdomains:
default language -> domain_A.com (works as expected, no prefix, correct links)
translation 1 -> hreflang1.domain_B.com (404 on category archive)
translation 2 -> hreflang2.domain_B.com (404 on category archive)
This issue will be solved in our next version or Yoast SEO Multilingual. However, if the workaround does not work for you, don’t hesitate to open a ticket in our support forum so we can check your situation carefully.