TYPO3 Core

Armin, I suspect that this might be the same bug that is fixed by https://review.typo3.org/#/c/53739/. Could you be so kind and check that? :)

I've digged into the getSortNumber method and tried to understand what happens.

So the mayor difference, is that the records used for calculating the sortNumber are differently selected.

When I translate three content elements from default language:
1. Checks sorting from first default record ($row) and its next sibling ($subrow)
2. Calculates new sortNumber ($sortNumber = $row[$sortRow] + floor(($subrow[$sortRow] - $row[$sortRow]) / 2);)
3. Create new translation record with calculated sortNumber
4. For the second record to translate, it compares the recently created record ($row) with the original sibling ($subrow), calulates and create new translated record
5. For the last record it also uses the recently created translated record and compares it still with the original sibling

When translating from a foreign language it behaves the same, but for the last record it uses NOT the latest translated record as $row, it uses the one before. The $subrow is the sibling of the latest translated record, which is (in this case, because of 3 items) the recently created translated record.

Long story short: I guess this happens because of negative PID voodoo. The pid is the only criteria used to calculate the sortNumber (besides existing sortNumbers itself). And localize in DataHandler seems to set pid to a negative value, which affects the sorting algorithm.

Okay. After debugging a lot, I've found the point where it goes wrong:
\TYPO3\CMS\Core\DataHandling\DataHandler::getPreviousLocalizedRecordUid

In the query just default language is checked, to fetch sortings of records.
When you enter the $language variable, it works.

For translations from default AND from foreign language.

Patch set 2 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55508

Patch set 1 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55509

Patch set 2 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55509

Patch set 4 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55486

Patch set 3 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55508

Patch set 4 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55508

Patch set 5 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55508

Patch set 6 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55508

Patch set 7 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55508

Patch set 8 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55508

Patch set 9 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55508

Patch set 10 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55508

Patch set 11 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55508

Patch set 12 for branch master of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/55508

Patch set 1 for branch 11.5 of project Packages/TYPO3.CMS has been pushed to the review server.
It is available at https://review.typo3.org/c/Packages/TYPO3.CMS/+/72254