From Johan Jönsson:
So I've encountered this enough times lately that I thought I could at least pass it on. You know far more than I do, of course, and might have data that make this relevant, but nevertheless, passing on some feedback:
Several of my friends and acquaintances have had problems adding languages. They use the iOS app in Swedish. All of them also want to search in English – else the app is far, far less useful in Sweden – and some in additional languages. They don't connect the "more" ("mer", in this case) to the (one) listed language, and don't understand they can click it to add more ones. Once they have more than one language it's obvious to them what it does; when there's just one language listed under the search field they don't understand it's the potential start of a list and thus not the function of the link. Their request has been to rename it to something like "more languages" (although very long in English and some other languages, of course), or possibly "languages" instead of "more".
Proposed design solution
Add a tool tip to the search screen under the 'More' link to encourage users to add additional languages
Title: Add languages
Body: Search Wikipedia in nearly 300 languages
The popover would appear once for users who have only one language selected on their first view of the search overlay.