Web browsers are for serving website content, their job isn't to moderate content especially at the level you're describing. If you want to write your own filter/extension to preserve your eyes from being exposed to unfamiliar words, you're free to do so.

Wikipedia has Simple English - https://simple.wikipedia.org/wiki/Simple_English_Wikipedia - maybe you're looking for something like that.

But the idea that we should be discouraging difficult words, or that this should be done at a browser level is terrible in many ways.