Important: #85560 - Location of XLF labels changed 

See forge#85560

Description 

Downloaded files for XLF language files are usually stored within typo3conf/l10n. When the environment variable TYPO3_PATH_ROOT is set, which is common for all composer-based installations, the XLF language files are now found outside the document root, available under var/labels/.

The Environment API Environment::getLabelsPath() resolves the correct full location path prefix.