[5.2] Languagefilter: Add message when no content language is published

[Hackwar]

Pull Request for Issue #41798 .

Summary of Changes

When you unpublish all content languages, but have the languagefilter system plugin enabled, the system is in an undefined state and different errors can show up. This PR adds a constant message to all pages that the administrator has to take action here.

Testing Instructions

1. Unpublish all content languages
2. Enable the languagefilter plugin

Actual result BEFORE applying this Pull Request

See nothing, maybe PHP notices from the languagefilter plugin.

Expected result AFTER applying this Pull Request

See a message that the content languages are disabled and the languagefilter plugin is enabled.

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

[Quy]

I have tested this item ✅ successfully on 4e5629b

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[ChristineWk]

I have tested this item ✅ successfully on 4e5629b

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/43232.}

[Quy]

I have tested this item ✅ successfully on 352b86f

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/43232.}

[ChristineWk]

I have tested this item ✅ successfully on 352b86f

---

_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/43232.}

[Quy]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/43232.}

[woluweb]

txs @Hackwar!