What I mean by "progressive" language learning:
The student starts by learning a small amount of vocabulary and grammar.
When practicing the foreign language, the student replaces the native words that he/she knows, e.g.
I learn German -> Ich learn Deutsch.
The student then learns more vocabulary and grammar.
After the student has learned enough words, he/she can start speaking less native words.
Steps 3 and 4 are repeated until the student can speak the foreign language fluently.
This is similar to how Toucan works, but as one uses it for longer, the number of native words will not decrease.
