We use the Woodmart theme which comes bundles with the "HTML blocks" plugin. We have always managed to create an HTML block in English and find the shortcode for the block in the WPML String Translation (and translate it from there).
However right now our HTML Block shortcode is not showing up in the WPML string translation, and I do not know how to search for it. The search yields nothing. Solution: You can add the shortcode translation via translation editor.