[TASK] Deprecate further l10n_mode usages

This change is focussed on runtime processing of l10n_mode
which is not required anymore. Thus accordant internal
functionality is deprecated.

Change-Id: I19b8eabdfc98bfe83ff80d8205b0c9f029330ed5
Resolves: #80345
Releases: master
Reviewed-on: https://review.typo3.org/52013


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>