Some Italian lessons titles use the wrong verb tense

[Cryptomane]

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• Bug report
• Feature request

Issue description:
Titles for lessions 4-5-8-9-12-14-18-19-22-23-24-25-27 are currently translated using the gerundio tense, however that makes them sound awkward as it's not appropriate to the context. The current translations like Lesson 8: "Definendo Le Tue Variabili" should be either "Definire Le Tue Variabili" or "Definisci", preferably the first one.

In short, when the title is about "something-ing" stuff the Italian translation should use infinito tense or indicativo presente tense instead of gerundio.