Geez, stop leveling up so fast!!
just kidding :p
Yes, we know that the level-up pop up message is untranslated right now, but that's because we (GaoGaiGirl, Logress, Lupos and me) are still trying to come up with the messages!
Originally, Japanese GMs came up with the messages, and each of them is very unique and funny, so we decided to make them by ourselves for the U.S. Iczers. In short, yes, the messages will be in English.
But thank you for pointing it out!