<translate>…</translate> and the related <tvar>…</tvar> are currently un-parsed and shown as plain wikitext in VisualEditor because they're not recognised, per T50891; however, once that is fixed, the blocks won't be editable except as alien nodes (in wikitext), and won't be createable.
Making a proper VisualEditor plugin to translate these in-page as a rich editor shouldn't be particularly hard (he says…).