The wiki page translation feature of the Translate extension does not currently work with VisualEditor due to the special tags it uses. More specifically, this is about editing the source pages that are used as the source for translations, not the translation process itself. The work can be divided into three steps:
Migrate the special tag handling to a more standard way to handle tags in the parser. This need some changes to the PHP parser for it to be able to produce wanted output.
Add support to Parsoid and VisualEditor so that editing page contents preserves the structures that page translation adds to keep track of the content.
Add to VisualEditor some visual aid for marking the parts of the page that can be translated.
This is likely to be a difficult project due to complexities of wikitext parsing and intersecting multiple different products: Translate, MediaWiki core parser, Parsoid, VisualEditor.
Mentors: general #VisualEditor plugins mentors + Niklas Laxström