Hello there,
I would like to apologize in advance for the log delay.
Basically you can change the get_search_form(false) line which prints the search form HTML with this code block:
<form action="/" method="get">
<label for="search">Search in <?php echo home_url( '/' ); ?></label>
<input type="text" name="s" id="search" value="<?php the_search_query(); ?>" />
<input type="image" alt="Search" src="<?php bloginfo( 'template_url' ); ?>/images/search.png" />
</form>
But it’s a bit complicated for non-coder. To easiest alternative is to translate the “Search” string using Loco Translate plugin. Once this plugin is active, navigate to Loco Translate > WordPress, setup your current language and then search the string “Search” to translate.
For more comprehensive instructions, checkout this documentation.
Regards,
Kharis