[Waiting for user feedback] Other languages not showing on the language switcher

Thanks for your reply. Let me try to answer your questions accordingly since it is related.

1. How can I determine which is the default language of a page or post?
A default language page does not have the "This is a translation of" indication as shown in the attached screenshot.

2. How can I determine that all translated pages are connected correctly to this default language page?
You can check the "This is a translation of" option if it's pointing to the primary language page which you've identified on #1.

3. How can I determine that all translated pages are published?
There is no indication in the Translation Management and you'll need to check this manually.

4. On the top of the pages I see the different languages and behind it in round brackets the number of pages published. How can I determine quickly which pages are missing?
You can check the primary language English and if it's not showing the "pencil" icon, it means it is not fully translated. Untranslated pages will not display on the frontend

5. Sometimes when I want to edit a translated page it pops up the regular "edit post/page" screen whereas other pages the "advanced translation editor" is fired up.

How is that possible? The translated pages that opens up with the regular "edit wp post/page" screen are correctly connected to the original page as laid out by your steps.
I'm not sure what you mean by this. Could you elaborate?

Example page where the regular wp post/page opens up:

Whitepapers & use cases — Elementor

Here the Auto Translated Editor fires up correctly:

Customers - Elementor

6. Another thing is that the slugs of many pages need to be corrected.

When I do that by editing that in the "wp edit" mode will that disrupt the connection between the original and the translated page?

Or is there a better way to correct the slugs?
To translate the URL slugs manually, navigate to WPML > Settings > Translated documents options > Page URL > Change to "Translate (this will include the slug in the translation and not create it automatically from the title)"

Thanks for your reply. I understand what you mean now.

When editing a translation opens the default WordPress editor, it means that the page is currently set to use manual translation (WordPress Editor), as shown in the attached screenshot.

To fix this, you just need to switch the translation method to WPML Translation Editor on the primary language page.

You can follow the steps explained here:
https://wpml.org/documentation/translating-your-contents/using-different-translation-editors-for-different-pages/

Thanks for your reply. That option will only appear on the primary language page English hidden link . I hope this clears it up.

Thanks for your reply. I can see it on your Website as shown in the attached screenshot. Are you not getting this? Please make sure you're on the primary language, English.