Does "infinite one" really mean "無限の mugen no" in japanese? I was using Google translate and Wordhippo?

Ben

No. 無限の means "infinite". It is an adjective (specifically the attributive form). The simplest way of saying "infinite one" (assuming the "one" is a being of some sort) would be 無限者 (mugen mono or mugensha). I, however, would favour the more poetic 無限なる者 (mugen naru mono). なる is an archaic way of conjugating certain adjectives, and sounds more poetic to modern ears.