indeed, I said it's At Least Genius only because EG is not just above peak human but it is way above it, so I'm not sure if just learning a language very fast is EG alone but this dude is apparently a newborn which makes the feat more impressive.
I just want to point out is that Eg has few other requirements such as being good in many fields so just "learning languages fast" alone may not be enough to qualify, it would be good to have more feats other than just this.
Super Mega Hyper Smart Dude
I see that makes sense, I will try to come up with something. The things that come of the top of my head are that:
1. He was able to learn Japanese in just 1 day.
2. After anther parasyte transformed he correctly deduced its weakness and accurately hit him and took its heart.
3. Just by talking to another parasyte he deduced that he did not see his host as a threat and created an strategy to kill him by pretending to be attacking him while his host kills the parasyte.
4. He managed to save shinichi by performing surgery on his heart with limited tools, I believe his knowledge about the human body allowed him to save his host(Shinichi) and himself.
5. Should have a better Analytical Prediction to another parasyte in the series who predicted that his opponent was going to pierced his host's heart.
6. He attacks after he anticipate every possible future move of his opponent.
7. Can determine someone's strength simply by looking at them.
8. Managed to drive a car just by reading about it and accurate hit a car in the lower part of the mountain which was moving.
9. Managed to fight someone who is 5 times as strong, faster, and has precognition, just by pure skill.
10. Came up with a plan to kill him(the parasyte who is 5 times stronger) while being tired, separated from his host(weakened), and under fear; it would have worked but he was not strong enough.
Those are the things that come to my head. I think there is more, but I need to get the scans for it and present my arguments correctly.