Actually, the most important for me would be
- 2+ notebooks per language
.., because only 1 notebook would become too long, messy, and unmanageable in just a few weeks.
On day one, I would create distinct notebooks for:
- Main
- Idioms
- False friends and Co
- Verbs
- South-american Spanish (the variations)
Per notebook, I’d like to have:
- a [
Search] function, with autocompletion - a T.O.C. or outline
- An [
/
] - [read-only/edit] toggle, to protect the contents - Auto-save and [Restore to previous version], because shit happens
- navigate with a sidebar slider (vital once you have more than 10-20 pages)
For the notebook editor:
- [Insert page breaks] and pagination, for structure and readability
- [Copy/Move to <other notebook>], for cleanup and maintenance
- Highlighting, images, hyperlinks, bullets, fonts, etc..
- [
jump-to-source], for text blocks (words with context) that were copied from a lesson
At the lesson level, I’d like to have:
- A list of the associated notebook(s)
- A
icon and link next to words/sentences that were copied to a notebook
That would be a good start 
