Translate API: never return empty string for translation of "Continue"

[tobifjellner]

The ​http://api.wordpress.org/translations/core/1.0/ includes a translation of the string "Continue" that is used during selection of new language for a WordPress site. This string is fetched from the corresponding core/dev/admin translation of the string "Continue". Some locales, where the translation haven't been maintained for a while, were lacking a translation. In those cases the API was sending an empty string, which would then render as an empty button in the user interface.

See ​https://core.trac.wordpress.org/ticket/48776

My suggestion is that instead of patching this in Core, we should make sure that the API never sends an empty string as the translation of "Continue".

[ocean90]

The API returns the translation of the string. If there is no translation no other string should be returned.