What are the most difficult things to learn in the Modern Greek language?

To Tasos Anesiadis’ answer (Tasos Anesiadis’ answer to What are the most difficult things to learn in the Modern Greek language?), I’ll add for Modern Greek:

• The chaos introduced by the clash of spelling pronunciations from Ancient Greek (via Puristic), and vernacular pronunciations. [nd] vs [nð]; clusters like [fθr]; [i] vs [j] before a vowel (άδεια, two syllables as “empty”, three syllables as “day off”).
• The subtler points of when to use the subjunctive (e.g. θέλω αυτοκίνητο που [να] κοστίζει 100 χιλ ευρώ I want a car which costs €100k vs I want a car which should cost €100k—the former implies you have a specific car in mind, the latter is a generic reference).