[Resolved]

Problem:
You are trying to translate text from English into multiple languages using the Advanced Translation Editor in WPML, and encounter an error when manually translating large segments. The issue arises because markers in the English text box, specifically 'wpml_linebreaks', cannot be implemented in the translation, preventing the text from being saved.
Solution:
To address this issue, ensure that the number of newlines in the original content matches those in the translated content. You can use the "Copy" icon within the segment to copy the content exactly from the original and then proceed to add your translation. This method sets the necessary markers correctly. Additionally, be aware that the visibility of 'wpml_linebreak' as a marker will be removed in an upcoming update of our editor, which is currently under quality assurance testing.

If this solution does not resolve your issue, or if it seems outdated or irrelevant to your specific case, we highly recommend checking related known issues at https://wpml.org/known-issues/, verifying the version of the permanent fix, and confirming that you have installed the latest versions of themes and plugins. Should you need further assistance, please do not hesitate to open a new support ticket at WPML support forum.