It seems barely readable, what editor do I need for this?
That is a manual page. You can view it by downloading the file and doing this command in a terminal window (assuming you're on a UNIXy system like Linux or Mac OS X):
You can edit it with any text editor.
A little bit of extra info:
Man pages all end in the extensions
*: List of sections from the Wikipedia page on man pages.
Technically, it's plain text, i.e. any text editor can edit it. As for what it's saying... It looks like some sort of scripting language, but not one I recognize. From line 365,
As an aside, file extensions don't really mean anything. They're just a "rule of thumb" for determining file types. A lot of plain text files either have no extensions or "unconventional" extensions, like .old or .bak for backup copies of files, or .1 for file one.