All that glittlers isn't gold

This popular saying means the attractive external appearance of something is not a reliable indication of its true nature.

The Spanish version goes "No todo lo que brilla es oro". Literally, not all that glitters is gold.

Note that the English version can be understood like "Every object that glitters fails to be gold." Thus, actual gold must not glitter. Maybe when Shakespeare wrote the line for his play "Merchant Of Venice", he wanted the rhythm: ALL that GLISters IS not GOLD and he was unconcerned with the exact meaning of what he was
saying.

The Spanish version, phrased negatively, captures the logical intended meaning quite well.