qtrans_getLanguage() raises error 500

Hi Community, I do really hope you have a good idea ??

The WordPress installation is running on a server with PHP 7.2.
qtranslate is running quite well (with the standard fix for 7.1) so far, but I am having trouble with my theme (self made).

In my functions.php I have the following script to always show the excerpt addition, even when the text is already small:

function excerpt_more_link_all_the_time() {
	// Remove More Link from get_the_excerpt()	
	function more_link() {
		return '';
	}
	add_filter('excerpt_more', 'more_link');
	//Force read more link on all excerpts
	function get_read_more_link() {
		$excerpt = get_the_excerpt();
		return $excerpt.' ...<br><br><a class="btn more_btn" href="'. get_permalink($post->ID) . '">Erfahre mehr</a>';
	}
	add_filter( 'the_excerpt', 'get_read_more_link' );
	
}

I was now trying to make it multilinual by telling the script to either show “Read more” for English and “Erfahre mehr” for German.

I tried:
_e("<!--:en-->Read more<!--:--><!--:de-->Erfahre mehr<!--:-->")

which did not work at this part of code (working fine on other parts of the template),
and I tried:

if (qtrans_getLanguage() == 'en') { $more = "Read more";}
if (qtrans_getLanguage() == 'de') { $more = "Erfahre mehr";}
return $excerpt.' ...<br><br><a class="btn more_btn" href="'. get_permalink($post->ID) . '">'.$more.'</a>';

But this instantly raises an server error (Error 500).

I also tried already to set up separate function.php files for each language, but calling then using qtrans_getLanguage() also ends up in Error 500.

Anyone any idea?