Within the UrlLinkEnhancer, the current language is obtained by $this->languageManager->getCurrentLanguage() and used to help build the public-facing URL for a link. Drupal's default behaviour is that this language is the one negotiated for user interface text and not necessarily the same as negotiated for content being returned.
This came to light on our decoupled project where the CMS user interface uses a fixed language, but content uses language negotiation over URL prefix. We found that all link field data returned by JSON:API had a path prefix of /en/ (our default language).
The current content negotiated language can be obtained by passing a type parameter as per:
$url = Url::fromUri($data['uri'], ['language' => $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)]);
Patch to follow.
Closed: duplicate
3.0
Code
Correcting error of missing use statement in previous patch.
Hey @Paul_Gregory ! Seems a duplicate of ✨ URL for link enhancer uses arbitrary language type (interface) Needs review right?
@budalokko My apologies, it is an exact duplicate. Not sure how I missed that.