[5.3] Improve System - Language Filter plugin code

[joomdonation]

Pull Request for Issue # .

Summary of Changes

This PR improves System - Language Filter code:

• Add missing $event parameter to event listener methods. Also add void return type declaration to these methods (all event listener methods should have void return type)
• Introduce $app and $language variables to avoid repeat calling methods to get these objects
• Fixed a small bug with onPrivacyCollectAdminCapabilities does not return data properly. It needs to use $event->addResult to return data instead of return command. I will backport this bug fix to 5.2 if required

Testing Instructions

• Expect to have at least one code review from maintainer
• Setup a multilingual website using Joomla 5.3 nightly build, apply patch, navigate to random pages from frontend of your site and make sure nothing is broken.

Actual result BEFORE applying this Pull Request

Works

Expected result AFTER applying this Pull Request

Works, code is better. A small bug is fixed.

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• No documentation changes for manual.joomla.org needed

[Fedik]

I have tested this item ✅ successfully on f54e47a

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[richard67]

Hmm, with this PR applied, all was working during my tests, but I got a PHP warning which I do not get without this PR applied:

PHP Warning:  Attempt to read property "sef" on null in /home/richard/lamp/public_html/joomla-cms-5.3-dev/plugins/system/languagefilter/src/Extension/LanguageFilter.php on line 278

I get this when using the button in the backend for going to the frontend or when using the site URL without any language suffix appended, i.e. the pure domain only.

Update: And I get it only when having this PR here applied and in addition PR #44844 for the debug plugin. Weird.

Update: Ot happens also when I apply only PR #44844 but not this one here. Will report in PR #44844 .

[richard67]

I have tested this item ✅ successfully on f54e47a

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[richard67]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/44841.}