In dewiki (wmf.1) Suggestions on Special:ContentTranslation display a standard thumbnail image when an article does not have an image to display :
<div class="cx-selected-source-page__image oo-ui-iconElement-icon oo-ui-icon-page-existing"></div>
In testwiki (wmf.3) - the placeholder thumbnail image is missing:
Note: the issue is present for other languages too.