Well, JK, it's true Japanese doesn't have much of an accent, and the vowel sounds are simple, but it's difficult for English speakers to speak it naturally precisely because it doesn't have an accent. : )
When Mika spoke Japanese, it was quite flat and natural, maybe more so than Marty.
Also, there are certain sounds that don't exist in other languages.
Anyway, Sou, "Please teach me Japanese." is, "Nihongo-wo Oshiete Kudasai. Nihongo=Japanese Oshiete=teach Kudasai=please