This extension brings standard labels such as week days and month names to your fingertip.
Within your extension, you may use the standard TYPO3 API to fetch localized labels.
For Backend usage:
$GLOBALS['LANG']->sL('LLL:EXT:locales/Resources/Private/Language/locallang.xlf:day.full.1');
For Frontend usage:
$GLOBALS['TSFE']->sL('LLL:EXT:locales/Resources/Private/Language/locallang.xlf:day.full.1');
Have fun, and please contribute to the translation on https://translation.typo3.org/projects/TYPO3.ext.locales/