Thanks for reporting.
I see your code and it looks plausible. But I cannot replicate your issue.
Which Joomla Version? Which language are you using?
Could you describe waht you did exactly and maybe add a screenshot?

Hi,

he error occurs in any language version Joomla 6.1.2, including the default English version, when you create your own administrator menu and then try to edit the Components container in that custom menu.

Steps to reproduce:

Menus → Manage
Select: Administrator
Click New
Title: My admin menu
Unique Name: my-admin-menu
Select Import a Preset: Preset - Joomla Main Menu
Click Save & Close

Content → Administrator Modules
Open Admin Menu for editing
Select Menu to Show: My admin menu
Click Save & Close

Menus → My admin menu
Open Components for editing, the following error occurs: Call to a member function load() on null

In the file: /administrator/components/com_menus/tmpl/item/edit_container.php the $lang object is used on line 65, but it is not initialized anywhere in the file.
It should therefore be sufficient to initialize the $lang object near the beginning of the file, e.g.: $lang = $this->getLanguage();
I have successfully tested this fix both by modifying the file directly and by creating an override in the Atum template. Until an official fix is available, I am using the template override.

Regards
Standa

confirmed the bug - thanks for the detailed instructions in how to replicate it

As you have a fix are you able to submit a pull request with the fix please

As it didnt look like you were going to create a pull request I did it for you

Please test PR #48252. Thanks.

@QuyTon why did you delete this issue? The practice now is not to delete an issue just because a PR is created.

This must have changed while I was not active with Joomla. Sorry I did not know. I will stop closing them. Thanks.