InvalidArgumentException: Invalid translation language (en) specified

Can you give some more steps on how to reproduce this? I have an entity already created in english which is my default language. I've added a new language (spanish). Should i change default language here: /admin/config/regional/language to spanish? I tried that and edited the node but didn't see any issues. There must be some other configuration steps i'm missing.

Wasn't able to reproduce but looking at the patch now and seeing the default type, it totally makes sense for your fix so I'm merging. Thanks for the patch!

Ah, sure. I guess "if interface and content language differ" is indeed to vague.

Something like this:

(The "Selected language" is identical for both interface and content, as-in they share the value, set to default site language).

Point is to get to active language for interface and content to differ, one way or another.
That this can happen is often overlooked, both in core and contrib. Core does not always separate interface and content properly either, many issue about that.

Just imagine, you have editors with different native languages, and they each one wants to have the interface in their own preferred language (hence the "Account administration pages" enabled for interface) but they all managed content in all available languages.

So, in my specific case, I tried to edit an existing node with custom field with only NL translation (source) while having the interface forced to EN.
In that case, the code (pre) patch would use EN as default language to load the entity in for access checking, while it might not exist (yet) in that language. The content language does return NL in that case, since we're indeed editing the entity in that language.

PS: While trying to post the commit, the issue was already set to fixed. But submitting this anyway for future reference.

Thanks for the detailed explanation! Yes, i went ahead and already merged it: https://www.drupal.org/project/custom_field/issues/3508870#comment-16004809 🐛 InvalidArgumentException: Invalid translation language (en) specified Active

There's actually no guarantee there is a translation too for the entity. If not, it will crash

This is the current fix I have for now, but I'm not sure if it's the proper one. But at least it doesn't crash for now.

(which reminds me I should make a follow up for the formatter_settings crash, but close on a deadline atm)

diff --git a/src/Plugin/CustomFieldWidgetBase.php b/src/Plugin/CustomFieldWidgetBase.php
index 51e544cdf..00e5b26ea 100755
--- a/src/Plugin/CustomFieldWidgetBase.php
+++ b/src/Plugin/CustomFieldWidgetBase.php
@@ -112,7 +112,7 @@ public function widget(FieldItemListInterface $items, int $delta, array $element
       $langcode = $this->languageManager->getCurrentLanguage(LanguageInterface::TYPE_CONTENT)->getId();
       $is_default_translation = TRUE;
       $is_translatable = $field_definition->isTranslatable() && $field->getWidgetSetting('translatable');
-      if (!$entity->isNew()) {
+      if (!$entity->isNew() && $entity->hasTranslation($langcode)) {
         $entity = $entity->getTranslation($langcode);
         $is_default_translation = $entity->isDefaultTranslation();
       }

@swentel: What's the context of your case?
Inline entity form perhaps?

@andreas no, just regulary entity forms, created an issue at 🐛 Entity translation does not necessarily exist Active

@andreasderijcke, can you weigh in with a review on that patch in https://www.drupal.org/project/custom_field/issues/3510744 🐛 Entity translation does not necessarily exist Active please?

That patch makes indeed sense.

I'm just wondering if there are other situations where the current (content) language will not match entity (translation) being edited or created.

In my language (detection) setup, the $entity->getTranslation() is returning the default translation of the entity because of the fallback logic in \Drupal\Core\Entity\EntityRepository::getTranslationFromContext().
Any module affecting this fallback logic, could indeed lead to different result.