Well, let's just be glad she's not pointing the rifle at Mikan, while still having her finger on the trigger.
The author hasn't bothered to address the language issue in any manner. Mikan had a five years old little brat's language skills when she was transported to the other world. It means she wouldn't have reading or writing skills either, nor would she learn the Japanese writing over there. Her Japanese vocabulary would be polluted by an alien language even if she had autotranslate magic in effect because she wouldn't have been learning more Japanese, only the alien language. Yet she can speak normally, read, and write. The only real explanation would be that the fantasy world uses modern Japanese, for an unfathomable reason.
In practice, the author will never even attempt to explain it, I bet.