TYPO3 Core

Hey. Thanks for your report.

You need to be very careful with the "translation original" (l18n_parent / l10n_parent) field. It basically means that you're changing an element from 'copy' mode to 'translated' mode or vice versa when fiddling with it. This can easily lead to data inconsistencies, especially when relations are involved.

The core is basically built around the idea, when using 'translation mode', that there is always a default language element first. A transition from 'copy' to 'translation' for localized elements is pretty much not implemented and leads to side effects like you described above "my relations are gone".

This area is very hard to get right and I don't think this will change soon. I think, we'll rather try to hide / further restrict these elements in the editing views in the future. Since not only admins but also editors can create quite a mess fiddling with "translation original". This is similar for the 'language selector': The interface happily allows to change a content element from language 'one' to language 'two', which then can lead to the situation that there are two 'two' localization of a default language elements. Similar if you change an element form 'language two' to 'default' or '-1' - all these scenarios are not handled well in this system. That's a very long standing issue and we're trying to mitigate / resolve this mid-term since it leads to a ton of refactoring in critical areas.

I'm afraid to say situations like you described are known and take quite a serious amount of time to get right. There won't be easy upcoming bugfixes. We can only try to slowly improve the situation with younger major core versions.

Until then: Be very careful when doing this and avoid editing both sys_language_uid and l10n/l18n_parent fields in elements.