Hm... so far Malay is leading in the numbers of letters. However, Japanese writing is a troublesome in the whole scheme of things. Maybe this is worth checking out after all.

English: I found a cat. (10)
Malay: Saya telah menjumpai seekor kucing. (30)
French: J'ai trouvé un chat. (15)
Italian: Ho trovato un gatto. (16)
Italian dialect: Ho catà en gato (12)
Deutsch: Ich habe eine Katze gefunden. (24)
Swedish: Jag hittade en katt (16)
Japanese: 猫を見つけた (6)
Japanese (romanize): neko wo mituketa (14)
Serbian: нaшao caм　мaчкa (13)
nederlands: ik heb een kat gevonden (19)
rumantsch: jau hai chattà in min/in giat (17/18)
moujér(?): minkixän (?)