Looking at code, I think you should separate the query for published, and leave alone the code with if ($app->isSite() && JLanguageMultilang::isEnabled()) as this is done in the other search plugins.
I.e. should be:

        $query->where('a.published = 1');

        if ($app->isSite() && JLanguageMultilang::isEnabled())
        {
            $tag = JFactory::getLanguage()->getTag();
            $query->where('a.language in (' . $db->quote($tag) . ',' . $db->quote('*') . ')');
        }

I have tested this item ✅ successfully on c0b829b

I have tested in Joomla 3.5.1 and patch works perfectly.

I have tested this item ✅ successfully on c0b829b

It works perfect after applying path.
It has two successful tests, but as per @infograf768 suggestion, I agree that $query->where('a.published = 1'); should be outside of the condition. Also, I would like to suggest below code to use quoteName.

$query->where($db->qn('a.published') . ' = 1');

Thanks for fixes.

rtc

@brianteeman Please remove RTC, see comments by @infograf768 and @gunjanpatel .

Done

Back to pending

@EmilMassey

Please update your PR

This PR has received new commits.

CC: @gunjanpatel, @hardiktasol

I have tested this item ✅ successfully on db7e77e

Tested successfully.

As the previously tested PR has been updated and confirmed by @gunjanpatel I am setting this back to RTC

RTC

Thank you @infograf768, @gunjanpatel for your suggestions.

Merged :) Thanks very much!