In the Shortcode API, you can find a lots of examples how you can implement this. Here is a possible solution:
function download_shortcode( $atts, $content = null ) {
return '<a rel="nofollow" href="' . the_field('download_link',$atts['taxonomy'] . '_' . $atts['term_id']); . '" target="_blank">DOWNLOAD LINK 1</a>';
}
add_shortcode( 'download', 'download_shortcode' );
When used like this:
[download taxonomy=text1 term_id=text2]
The output would be:
<a rel="nofollow" href="/*The response from the function*/" target="_blank">DOWNLOAD LINK 1</a>
So, this function download_shortcode() should be in your theme's functions.php file, or in a separate plugin. The only problem here is that you can't pass php code there (inside, as content or as parameters), so you have to choose, add parameters to the shortcode (the taxonomy/term fields), or insert content between opening and closing [download][/download] shortcodes.