custom block title translation not displayed

To display the title translation on custom blocks, I had to do this:

function my_module_preprocess_block(&$variables) {
  if ($variables['elements']['#base_plugin_id'] == 'block_content') {
    $variables['label'] = $variables['content']['#block_content']->label();
  }
}

#2 works for me.

I just have added a check for empty titles to do not display these:

function my_theme_preprocess_block(&$variables) {
  if ($variables['elements']['#base_plugin_id'] == 'block_content') {
    if ($variables['label'] !== '') {
      $variables['label'] = $variables['content']['#block_content']->label();
    }
  }
}

#4 works for me

      function my_site_preprocess_block(&$variables) {
        if ($variables['elements']['#base_plugin_id'] == 'block_content') {
          if ($variables['label'] !== '') {
          $variables['label'] = $variables['content']['#block_content']->label();
          }
        }
      }

#4 worked for me as well. I just don't understand why that isn't the normal behavior within core when viewing a translated block.

Tried #4 as well -- this works as expected.

Just wanted to say that #4 worked for me as well ! Many thanks all!

Thanks for the patches!

Tested on standard install of Drupal 9.4.x and this is still happening. This is a bug, so changing category.

This is a duplicate of #3226452: Block title is displayed in interface language, block content in content language. Should be content language. and even though that is later it has more discussion of the problem so I am closing this as a duplicate. And adding credit over there.

Thanks!

As of Drupal 9.4.5 this is still happening. While it puzzles me why, #4 fixes this issue just like that.

In my case, it was because the blocks were from a View, and they are considered configuration, see #3549927: Streamline translation of Views block titles, custom menu titles, etc.: Allow Interface Translation.