Please replace the use of "mw-headline" in ContentTranslation's ViewTranslationPage.vue (Special:AutomaticTranslation).
The "mw-headline" CSS class is no longer used by MediaWiki (see https://www.mediawiki.org/wiki/Heading_HTML_changes), and will not be styled by the skins. I suggest updating the markup to the <div class="mw-heading"> structure described on that page, so that you don't have to maintain your own styles. The appearance of headings in the real article and a translated article is already a bit different:
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