Translated multicolumn-contents show up only in backend

[neufeind]

TYPO3 v10, EXT:multicolumn 5.1.1

Instance was upgraded from TYPO3 v8 to v10 in the past. For old records multicolumn-contents show fine in frontend and backend. But newly created translations show up in backend only.

Upon debugging the records successfully shown in FE/BE it turns out there are actually two translation-records:
tt_content 9775: t3_origuid 335, tx_multicolumn_parentid 331, l10n_parent 335, l10n_source 335
tt_content 9786: t3_origuid 9775, tx_multicolumn_parentid 9781, l10n_parent 335, l10n_source 9775,

The content actually being shown as editable in the backend here is 9786. But when rendering the contents in fromtend the tx_multicolumn_parentid 331 is used to fetch records inside EXT:multicolumn. It seems that from there 9775 being fetched first (in FE) the second record (9786) is overlayed.
When editing the multicolumn-contents in BE however the backend shows container 9781 (translation from 331) and therefor fetches 9786 which has tx_multicolumn_parentid 9781.

[neufeind]

Found no real "solution" yet, other than to create the second row by hand and adjust values sigh

[neufeind]

Digging further into this issue it probably seems to be related to "connected mode" for translations:
https://docs.typo3.org/m/typo3/guide-frontendlocalization/main/en-us/LocalizedContent/Index.html
I assume the issue would not occur with free mode, since there the containers in the translated page itself are the reference.

What happens is is that the frontend fetches the original multicolumn-record and from there looks for contents in the columns in the desired language. The backend uses the translated container-element as base and fetches contents from there.

As a quick workaround it seemed to be possible to create two records (one related to the original language, the other to the translation) and link them. But it showed that edits from the backend then don't show up in the frontend anymore.

For TYPO3 v10/v11 we consider and suggest looking into migrating contents to https://github.com/b13/container instead.