Show the full language label paths in the backend:
$TYPO3_CONF_VARS['BE']['lang']['debug'] = true;
In TYPO3 8, this is different:
$TYPO3_CONF_VARS['BE']['languageDebug'] = true;
See https://docs.typo3.org/typo3cms/extensions/core/Changelog/8.7/Important-71095-AddLanguageDebugModeToAllConfiguration.html