In English, it is perfectly fine to use expressions like "vocabulary trainer" or "grammar trainer" to denominate a certain type of software that offers interactive exercises (often in the form of drill and practice).
The publishing house PONS apparently uses the expression "trainer lessicale" to translate "vocabulary trainer": https://itunes.apple.com/it/app/pons-trainer-lessicale/id452121028?l=it
Interestingly, Google searches for the word "trainer" return very few results that concern the context of e-learning.
Does the use of the word “trainer” appear strange in this context?
Why do you think PONS chose "trainer lessicale" over "trainer di vocaboli"?