Hi,
If you want a pure plain-text format, check out Mografi's JLC Converter available on the
Extras page. Note that Mografi eventually decided to use the built-in editor for Jenny LeClue. But some other developers use it and seem happy with it. It's the simplest text format, but it still supports Conditions, Scripts, and Sequences since it was written specifically for the Dialogue System.
If you're looking for an outline format, you could use Neverwinter Nights'
Aurora Toolset. Its editor looks a bit like this:
(The Dialogue System also has an outline mode, if you simply want to use an outline mode instead of nodes.)
There's also Ink, but research it (and its
Dialogue System integration) before choosing that route. Ink works very differently, so the Dialogue System integration is different from the other integrations.
The other import formats all use node-based editors, including articy:draft, Chat Mapper, Twine, and TalkIt.