I am a native speaker of English, yet my knowledge of its grammar is almost entirely informal. Having said that, it seems to me that in the 1:1 translation, the object of ‘is’ is ‘gold that glitters’, rather than just ‘gold’, and its subject is ‘everything’ rather than ‘everything that glitters’, and that these are semantic differences, as the intended meaning is specifically about things that glitter. I hope someone more knowledgable can cite the relevant rules here, whether for or against this reading.

To avoid ambiguity (whether actual or merely perceived by me), I might say “Just because something glitters, it need not be gold”, but that is not much of an aphorism!