Good to know!

In new versions of TYPO3 some language files have been moved. They still are in the same extension like they were before, but now they are duplicated as locallang.#######.xlf at the project's root.

You do not have to translate these files again. Instead, take a translated version of the old file and use the “Upload file” interface in the project view, to upload the translations.

That way all fitting translations will be inserted automatically.