This does give me a swirl of ideas, but I can't really put my finger on any of them. This old sponge of mine, the creaky wheels are spinning something silly.
The one immediate thought I had: if I were to setup an "authoring" TiddlyWiki for maintaining multiple language versions of tiddlers, this is the way I would go.
A "host" tiddler for every "English content" tiddler (or whatever language) and every "translated content" tiddler (one for every language of interest).
The "host" tiddler is used to manage all of the "content" tiddlers, including the place to keep meta-data about the content: descriptions, todo's, history, whatever.
From that "authoring" TiddlyWiki, generate "language-specific" TiddlyWiki instances for any one language, and/or instances with multiple languages, with or without the "host" tiddlers.
Oh, another thought I have my finger on: kanban.
And for both of those thoughts: figure out a pretty interface for multi-column and multi-row version of this side-by-side thing.
Oh, another thought: tiddler-hosted side-by-side story rivers ...