I agree with everything you say, as long as one assumption holds: the language(s) being used are static, in the domain of the topic being discussed. If the only available method to express 1x20 vs 20x1 is colloquial English or arcane math, then the method you describe seems to be ideal.
On the other paw, I've already gotten good use out of taking an existing language structure (the subset of Lojban sometimes called Cniglic, which can be bolted-on to English), and extending it for my own purpose. Since it worked so well before, I'm willing to try it again, if the next-best option is what you describe.
Or, looking at it another way, I'm drawing on the Sapir-Whorf hypothesis, and am more interested in improving language as a tool of thought rather than a tool of communication.
"I estimate 5% odds of X happening" can mean at least two things:
* I have about 1-in-20 confidence that all future timelines from this point contain X, and about 19-in-20 confidence that none do.
* I estimate about 1-in-20 future timelines contain X, and 19-in-20 future timelines don't.
Looked at this way, the usual way of quantifying probability seems to be a lot like quantifying area - the first bullet-point by having a 1x20 rectangle, the second by having a 20x1 one. (This also seems valid for having, say, 50% confidence that 1-in-10 future timelines contain X.) It seems like it might be worth having an easy and understandable way to differentiate between these different forms of '5% odds', but any easy way I've been able to think of is barely understandable, and vice versa. Are there any existing standard ways to do this that I'm unaware of? If not, does anyone reading this have any decent answers?
I'm not opposed to coming up with a new word for personal use to help get in the habit of thinking in certain ways; such as bei'e in Lojban to remind myself to think of probability logarithmically. I don't mind doing the same with a word meaning 'such-and-such a fraction of future MWI branches', if that's the best solution, or even just a useful tool; I'd just like to know what the full range of useful approaches really are, first, and any potential loopholes therein or drawbacks thereof.