Content translation/Product Definition/Entry points

Surfacing lacking languages
On content pages, we will indicate to some users that the content is lacking in some languages.
 * We will surface lacking languages only to users for which we are quite sure they will be interested to contribute in that language (users that changed the UI to this language, or users that already contributed translations to that language).
 * Only languages for which the content do not exist will be surfaced, but not all of them will be. We don't want the lacking languages to make it hard to find those for which the content is available.
 * Languages for which the content is lacking and we surface will be presented as red links in the interlanguage links list (we may consider them to be grey if we don't want them to be that prominent).

Once the user clicks on a red link form the interlanguage list, a "New article" panel is shown as described below.

New article creation
The panel provides the following information:
 * Indication that the page does not exist in the selected language ("the page does not exist in Nederlands.").
 * Invitation to create the page ("Do you want to create it?").
 * Input field for the new translation title with with the current title of the page as a placeholder. If the user leaves the field empty, the translation will use the current page title.
 * "Create from scratch" action that will allow the user to create a new page with the given title on the selected language.
 * "Translate from X" action where X is the current language. By default, users will create a new translation with the current language (X) as source, and the selected language (the one in the red link) to be the target.
 * A second part of the button will allow to select a different source language from those for which the article is available. Clicking the triangle will open the ULS showing those languages for which the article is available, and selecting one will change the button text to reflect that.
 * An "X" icon in the top-right area will allow to close the panel (note that this is not in the prototype).