notadictionary.com
死んだら棺桶にポップコーンの種入れて欲しい 火葬の時弾けるやん
→ “If I die, I want popcorn seeds put in my coffin. They'll pop during cremation, right?”
死んだら shindara = if (I) die (conditional form of 'to die')
棺桶 hitsugane = coffin (noun)
棺 hitsugi = coffin / sarcophagus
桶 oke = bucket / tub
に ni = in / into (location/direction particle)
ポップコーン popukōn¹ = popcorn (loanword from English)
の no = 's / of (possessive/genitive particle)
種 tane = seed (noun)
入れて irete = putting / inserting (te-form of 'to put in')
欲しい hoshii = want (adjective expressing desire)
火葬 kasō¹ = cremation (noun)
火 ka = fire
葬 sō¹ = funeral / burial
の時 no toki = when the time comes / at the time of (phrase indicating a specific moment)
の no = 's / of (possessive/genitive particle)
時 toki = time / moment
弾ける hajikeru = will pop / burst (future/informal of 'to pop')
やん yan = right? / isn't it? (sentence-ending particle for emphasis/agreement)