Sorry: there are some "spurious" commits above this one as I did some mistake in my local repo, but it seems to me that, having reverted the spurious ones, everything should be OK here.

Is there a way to get rid of that garbage I involuntary created? Thanks to whomever will help...

I botched the title of this PR. It should had been:

Language filter: use HTTP 301 status code for redirect instead of 303

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Please, see #5109 as well: they go somehow together...

Sorry, guys, I have changed everything: the main purpose of this PR is now trying to get rid of the Language Cookies.
This should be tested with the new proposed version of the Language Switcher
Used with it I see no reason to use HTTP 301 status codes on redirect

To get rid of the lang cookies, here is a patch:
#4911 (comment)

BUT it must be clear that getting rid of the language cookie means that it is ALWAYS the default site Language or the Browser settings that will be used when going back to the bare url without language code. That is mist of the time unwanted.

Could you please provide an overview of what this patch hopes to achieve, what we should see before the patch is applied, and what would show a successful test? It would help enormously for testers who don't know what you're proposing to fix.

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@RCheesley
Ruth, as it is now, this PR is just an opprobrium I'm very quickly going to close.
Its only reason to exists was to test #5109 which is "the real thing"

Beside that there is an ongoing discussion if redirects from the language_filter (I.e. redirects for functioning but not canonical URLs) should return an HTTP status code of 303 (as it is now) or 301

I'm closing this PR.
Beside being an horrible kludge it is now useless: use #4911 instead and set "Cookie Lifetime" to "None".