Activate Scroll Translations in a space.

Configure Scroll Translations to set Japanese as default language and add English as a target language.

Crete a original page and add body text in Japanese.

Select English from Language picker and add the translation.

Add some messages in the comment field when you select the English page.
When you select Japanese from Language picker, you can see the messages in the comment area.

Select English again from Language picker and Click Edit under the message you wrote in the step 5.

Add some additional text to the existing message.

Select Japanese from Language picker to try to see the additional text you added in the step 7.
actual:
The body text of the original language page is duplicated in the comment field of the original language. Whole message you added in the step 5 and step 7 cannot be seen. 2) You can not edit any existing messages in the original language page any longer. it displays an error message that says "Failed to save the comment." when you try to save the revised messages in the comment field.
expected:
Text in the comment field of the target language page should be shown in comment field of the original language page in the step 8. 2) Existing messages can be edited in both the original and the target page.