Sync UI language selection with user profile settings

[Gpetrak]

This PR was created according to this issue: #14150

Checklist

Reviewing is a process done by project maintainers, mostly on a volunteer basis. We try to keep the overhead as small as possible and appreciate if you help us to do so by completing the following items. Feel free to ask in a comment if you have troubles with any of them.

For all pull requests:

• Confirm you have read the contribution guidelines
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• Make sure the first PR targets the master branch, eventual backports will be managed later. This can be ignored if the PR is fixing an issue that only happens in a specific branch, but not in newer ones.

The following are required only for core and extension modules (they are welcomed, but not required, for contrib modules):

• There is a ticket in https://github.com/GeoNode/geonode/issues describing the issue/improvement/feature (a notable exemption is, changes not visible to end-users)
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• PR title must be in the form "[Fixes #<issue_number>] Title of the PR"
• New unit tests have been added covering the changes, unless there is an explanation on why the tests are not necessary/implemented

Submitting the PR does not require you to check all items, but by the time it gets merged, they should be either satisfied or inapplicable.

[gemini-code-assist]

Code Review

This pull request implements a user language preference system by introducing a new ProfileLanguageMiddleware, updating the profile form and admin interface, and adding a view to handle language selection. Feedback focuses on ensuring the user profile remains the source of truth for language settings, avoiding constant duplication, and persisting language changes to the database for authenticated users.

[codecov]

Codecov Report

❌ Patch coverage is 80.53097% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.60%. Comparing base (94ca636) to head (0b73f6e).
⚠️ Report is 13 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #14151      +/-   ##
==========================================
- Coverage   74.62%   74.60%   -0.03%     
==========================================
  Files         958      959       +1     
  Lines       57891    58282     +391     
  Branches     7889     7966      +77     
==========================================
+ Hits        43202    43482     +280     
- Misses      12927    13024      +97     
- Partials     1762     1776      +14     

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