Important: #71095 - Add language debug mode to All Configuration¶
See Issue #71095
Previously it was possible to set: $TYPO3_CONF_VARS['BE']['lang']['debug'] in order to enable debug in LanguageService.
However this could not be configured in the install tool. In order to enable this possibility it has been renamed to $TYPO3_CONF_VARS['BE']['languageDebug']