Being a Muslim means submitting one’s will to God. Adam submitted to God, so in that sense he was a Muslim.
Circumcision is not what makes someone a Muslim. According to Islamic tradition, circumcision was practiced by Prophet Abraham later. The Prophet Muhammad ﷺ said:
“Abraham circumcised himself when he was eighty years old.” Sahih al-Bukhari
As for language, Allah knows all languages. The Qur’an was revealed in Arabic because it was sent first to an Arabic-speaking people:
“We have not sent a messenger except in the language of his people, to make things clear for them.” (Qur’an 14:4)
Duʿāʾ can be made in any language. There is no requirement that personal supplications must be in Arabic. Allah says:
“And among His signs is the diversity of your languages and your colors.” (Qur’an 30:22)
So no, Muslims do not believe Allah only knows Arabic. Allah is the Creator of all languages and understands every word spoken by every human being.