Editing of translated pages in multiple tabs removes language from the editor

 *Steps to reproduce*

• Create a space with two languages: English (default), German

• Create a page in English with title "english" and content "english content"

• Translate that page into German with the title "german" and content "german content"

• Open the page in the first tab in English

• Open the page again in the second tab in German

• Go to the first tab and click "Edit" on the page in English

• Go fast to the second tab and click "Translate" on the page in German

First tab opens the editor with the english content. Second tab opens the editor with the german content and then reverts it to english (see IVSN-4568)

• Go to the second tab and append "additonal text" to the content and save.

Error message "The language of this editor has been changed. Save your work in a file and reopen the editor" is shown. Update button is disabled.

• Go to the first tab and append "error message" to the content, wait a bit and leave the page by going to the home page.

• Go to the second tab, select "German" as the current language and click "Translate". You will see the "Unpublished changes without language" dialog. 

• Click on "Discard all changes" 

• Click on "Translate" again.

Editor with German content is opened, BUT the title is from the English content. 

• Add more content to the page and save.

Page with english title and german content is saved.

Expected
You should not be able to "Translate" as the page is already edited in english.

Workaround

Do not edit pages with the same user in different tabs.