TYPO3 Core

Expected: The button in the modal should be "Gem og luk" (in Danish)
Actual result: The button in the modal returns "Save and close"

As far as I can see, it's the TYPO3.core.core saveAndClose label.

There is a "saveAndClose" label in file EXT:core/Resources/Private/Language/locallang_common.xlf (in TYPO3 v9), are we speaking from this one?

I can see that the label excists in the l10n folder as translated.

So you have a proper translation for this label? Then the problem does not seem to be for this project...

The problem also exists in German

Which problem? No translation for the dialog? Translated value available in directory l10n? No translated value available? In which file?

=> I expect more detailed information to track down the problem.

There is an missing translation for this button in
EXT:backend/Resources/Private/Language/locallang_alt_doc.xlf
and a wrong syntax in
EXT:backend/Resources/Public/JavaScript/FormEngine.js, where this translation would be required.
I'll add a patch immediately

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/58811

Applied in changeset 63995038a7217469f5ac91cdcb18b00e9bc54f60.