YOU SAID:
Hello, Mathis is very dumb
INTO JAPANESE
こんにちは、マティスは非常に愚かです
BACK INTO ENGLISH
Hi Mathis is very stupid
INTO JAPANESE
こんにちは、Mathisさんは非常に愚かです
BACK INTO ENGLISH
Hi Mathis is very stupid
That didn't even make that much sense in English.