"It is O.K in Japanese" is meaning "Please talk in Japanese."
"It is O.K in Japanese" is sometimes used when somebody said something in Japanese collapses.
For example,somebody said "Watashi no namae wo Yamada Taro desu."
It is miss for how to use "wo".
He had to use "Ha" when he said it.
Japanese is bery difficult,but you don't be afraid to use a Japanese.