TYPO3 Core

Did it have any side-effects in the database?
By looking into the code it should not have had any... (prefixLangTitle only for TCA types text and input)

if ($fCfg['l10n_mode'] === 'prefixLangTitle') {
    if (($fCfg['config']['type'] === 'text' || $fCfg['config']['type'] === 'input') && (string)$row[$fN] !== '') {

No effect in the DB, hence no bug-report.

I found that today, when I was looking at v8 and searching whether nav_hide is actually translatable. Which it is not.
Then I looked in v9 and found that it got no l10n_mode=exclude, hence it is translatable.
Benni suggested to add the sync feature to the fields, which I can agree with.

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/c/Packages/TYPO3.CMS/+/60891

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/c/Packages/TYPO3.CMS/+/60891

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/c/Packages/TYPO3.CMS/+/60891

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/c/Packages/TYPO3.CMS/+/60891

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/c/Packages/TYPO3.CMS/+/60891