Can't change translation settings for custom fields using the Multilingual Content Setup meta box

Overview of the issue

It is not possible to adjust translation settings for custom fields on the post edit pages. This is because the Multilingual Content Setup meta box was removed starting with WPML 4.5.0.

If you use ACF or any other plugin that relies on custom fields that need to be translated, you can still do that by going to WPML → Settings and scrolling to the Custom Field Translation section. If you need more details on how to achieve that please read our documentation about translating custom fields.

Workaround

As of WPML 4.5.3, you can enable the Multilingual Content Setup meta box by checking the box in WPML → Settings → Custom Fields Translation.