If this colored or underlined words past the 1000 rank, instead of removing them, it would be less offensive to my sensibilities.

Amusing coincidence that readams above used "up goer", as the "up goer" editor does what you suggest :

http://splasho.com/upgoer5/

That's actually a nice implementation. It's much easier to fix errors after finishing a sentence than it is to fear every word you type. Here's my attempt to describe compilers, which ended up going a little off-track:

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If you want to make new things for a computer, you first have to write them down in a way that a computer can understand. You have to use strange computer words, not normal human words. People usually only talk to other people, so talking to a computer using only computer words is very hard.

To make it easier, there are things that take human words and then write them out as computer words so you don't have to do it yourself.

Those things were made by people who went to school for a long time. To make them, they had to know all the human words and all the computer words too. Thanks to them, you can write stuff that feels pretty normal to you, and still be able to make new things for a computer. It's still a little bit hard, but you can learn the simple stuff in a few days.

A long time ago, only a few people could build new things for computers. But today, many people like you and me build them for money or just for fun on their free time.

Just imagine: you could build a whole new thing today. A thing that no one ever had before. And if the thing you build actually helps other people, you can get a lot of money for it. That's what many of us in the "Thing Building News" place do. We go there to share stories about the things we build.

I now want to thank the people who went to school for a long time and made the things that turn human words into computer words. They help us do easy and fun stuff for money.

:) That's pretty good, well done.

The first compiler took someone with a bachelor's degree in mathematics and physics from Vasser, a master's from Yale and a Ph.D. in mathematics from Yale and 3 years of experience with the machine.

And even then :

"Nobody believed that," she said. "I had a running compiler and nobody would touch it. They told me computers could only do arithmetic."

https://en.wikipedia.org/wiki/Grace_Hopper

Bingo - let users extend lingo and use crowd-sourced/maintained lingo/lexicon files.

It'd be absolutely awesome if these lexicon files evolved organically and were public over time to graph how language progresses...

I think even slang terms have a place here. Not sure if the goal is to really improve language skills. If not, any new widely accepted terms could be defined and optionally rated by a community for wider acceptance. If the word is fairly new it could be highlighted in some way to indicate its popularity.