Learn Greek from Brazilian Portuguese at PBC Languages

The first wall is sound. Brazilian Portuguese doesn't have θ (as in θάλασσα, 'sea'), δ (as in δάχτυλο, 'finger') or the raspy γ (as in γάλα, 'milk'). Most students substitute with 't', 'd' and a hard 'g', and Greek natives will understand you but correct you fast. The written accent (tonos) is not decorative either: πότε means 'when' and ποτέ means 'never', same letters, different stressed syllable, different word entirely.

Vocabulary works in your favor more than you'd expect. Brazilian Portuguese inherited hundreds of Greek roots through Latin, so words like democracia, teatro, filosofia or problema are recognizable the moment you see πρόβλημα or φιλοσοφία written out. The trap is assuming every look-alike behaves the same way in daily speech: ιδιωτικός looks like 'idiota' but means 'private', and συμπάθεια looks like 'simpatia' but leans toward 'compassion', not friendliness.

Grammar is where the calquing goes wrong. Portuguese dropped noun cases centuries ago; Greek still marks nominative, genitive, accusative and vocative on nouns and articles, so 'o livro' becomes different forms depending on its job in the sentence. Verbal aspect (finishing an action vs. describing it as ongoing) also splits Greek verbs into two stems, something Portuguese conjugation doesn't force you to think about. Where Brazilian speakers move fast is reading comprehension once the alphabet clicks: recognizing cognates in newspaper headlines or menus happens quickly, well before spontaneous speech catches up.