[BUGFIX] Transform language parameter when previewing translated pages

When previewing translated pages in the backend, URLs contain `&L=x` at
the end. This is due to a missing transformation into the `_language`
parameter as well a missing SiteLanguage resolving.

Resolves: #86421
Releases: master
Change-Id: I5da496d0224635b1ee849dd7a724145ad2c0d408
Reviewed-on: https://review.typo3.org/58438


Reviewed-by: Richard Haeser <richard@maxserv.com>
Tested-by: Richard Haeser <richard@maxserv.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Josef Glatz <josef.glatz@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>