[BUGFIX] Usage of sys_lang_mode in Typo3DbBackend

Due refactoring the property $languageMode is compared but is never
filled. The property from the querySettings has to be used.

Change-Id: I8f66a10548213513b8cc5a3a90cc219ed5f91918
Resolves: #54182
Releases: 6.2
Reviewed-on: https://review.typo3.org/25932
Reviewed-by: Markus Klein
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer