Strftimedammit is a single Vim documentation file that lists strftime-like formatting characters for a variety of languages.
It was born when I finally got sick of having to open a browser with the Django docs to look up how to use its date formatting template filter.
Install with Pathogen.
Make sure you
:call pathogen#helptags() after installing to make Vim notice
the new documentation file.
Now you can use
:help strftimedammit to open the documentation.
There are also tags in place for each language, so you can do
:help strftime-python or
:help strftime-django to go right to that
Add your favorite language to the doc file, fork, and send a pull request.