Do not show language spinner if dropdown has been removed

[swissspidy]

Noticed after working on #38664.

Core contains some code to display a spinner next to the submit button when selecting a language from the dropdown that has first to be installed. However, it does not check whether the dropdown does actually exist on the page, as some plugins do remove it & replace it with a custom solution.

We should prevent displaying a spinner in such cases as it's misleading. Plugins themselves can't do that because the JS is not easy to remove.

Core contains some code to display a spinner next to the submit button when selecting a language from the dropdown that has first to be installed. However, it does not check whether the dropdown does actually exist on the page, as some plugins do remove it & replace it with a custom solution.

This prevents showing a spinner in such cases as it's misleading.

The change can easily be tested by installing the Preferred Languages featured plugin and then simply saving the settings.

Trac ticket: https://core.trac.wordpress.org/ticket/57644

I think it would be too early.

But looks like the workaround in the PL plugin is way simpler than I thought: ​https://github.com/swissspidy/preferred-languages/commit/b3fb2d22139e56926a1ba09997e6605b81f81a18

So I'll just close this as a wontfix for now.

[swissspidy]

Plugins can work around this using CSS.