TYPO3 Core

Prerequisite TSconfig: mod.web_layout.defLangBinding = 1
TYPO3 is running in version 10.4.15

If defLangBinding is activated, the first "+ Content" link in a translated column is created with sys_language_uid = 0, not with the one that maps to that column.
Buttons that are created after an existing record do have the right sys_language_uid set that are forwarded to the wizard defValues.

\TYPO3\CMS\Backend\View\BackendLayout\Grid\GridColumn::getNewContentUrl creates wrong links in that case, $this->context->getSiteLanguage()->getLanguageId() returns always 0

I'm not really sure about the proper behavior of that setting judging from the documentation: https://docs.typo3.org/m/typo3/reference-tsconfig/master/en-us/PageTsconfig/Mod.html#deflangbinding

The old page module removes the buttons to add content in connected mode, whereas the fluid page module keeps them