In nearly every Webflow site, the navigation bar (including its dropdown menus) and the footer are Components. Their text is not part of any individual page — so sending a page, even the page where the menu "lives," will not carry the menu's items.
What to do: in Translate's content browser, open the Components group and select the navbar / menu / dropdown / footer components, then send them like any other content. The translation is applied to the component definition, so it takes effect on every page at once.
Two related details:
If a specific placement of a component has overridden text (e.g. the same card component with a different title on one page), that override travels with the page that contains it — translate the page too.
If menu entries are generated from a CMS collection (common for large "mega menus"), translate that collection in the Collections section.