What I did is upload a list of words in Turkish and German to Googlesheets and use this list as database. The shinyapp randomly pulls words from the list and remembers if I knew them or not (based on my input). This information is also stored in the Googlesheets. Depending how often you remembered a given words, this words will be stored in certain 'boxes'. Each word starts out in box 5 and moves down until box 1. Usually I only practice boxes 4 and 5 and only rarely check out the other ones.
The Excel file should contain the following columns:
original language
translation
optional: Lesson number (e.g. if you use a course book to learn the language)
Index
Box
Count (counts how often the app has shown you this word)
CountR (how often did you know it)
I hope someone can find some use in this! Have fun!