Translations of actions like "delete" and "edit"
A look at Wikipedia pages in other languages where imperatives are distinct from infinitives (as opposed to English where they are not) would suggest that words like "delete", "edit" and "log in" when referring to actions should be in the imperative mood (they do now seem to be consistently translated with infinitives). I propose we translate them with imperatives instead, in analogy with other Wikimedia translations. (I'd suggest specifically the aorist imperative to suggest a single, unrepeated action for most actions)
No! this is highly language/culture-dependant.
In French for example, the (impersonal) infinitives are highly prefered to the (personal) imperatives, and more formal (more polite: people don't appreciate personal orders, we only want to *suggest* them possible actions). And this consideration is not just for Wikipedia and social networks (Even Facebook and Twitter are using infinitives, as well as almost all online shops).
But these imperatives are also using a tone similar to commercial advertizing, that want to personalize their messages directly to the consumers...
Imperatives would be acceptable in other contexts such as online games (that favor a highly personal experience), but only during game play.
In support forums, the tone is adapted whever this is a personal question or assistance request (use imperatives when explaining guidelines for immediate problem resolution, or conditionals like "should" if alternatives are left to the user or not everything is known) or a general consideration (such as generic online documentation meant for all or intended to an open group of people).
Each time you target more than one people, you should use infinitives (so user interfaces uses infinitives everywhere in all applications, OS'es and devices).