Revert "merged branch jfsimon/issue-6928 (PR #7378)"

This reverts commit 70ec4f6c61a12000498790e70ca70a393ee03420, reversing
changes made to 3a03f3e346b12f330b6c1582d2f6d3bc7108d933.
[HttpFoudantion] fixed Request::getPreferredLanguage()
merged branch jfsimon/issue-7378 (PR #7438)

This PR was merged into the 2.1 branch.

Commits
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c928ddc [HttpFoudantion] fixed Request::getPreferredLanguage()
839c78a Revert "merged branch jfsimon/issue-6928 (PR #7378)"

Discussion
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[HttpFoundation] fixed Request::getPreferredLanguage()

Previous PR #7378 was wrong and adding BC break. Resolution for short languages codes is now done in `Request::getPreferredLanguage()` method.

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7378