There's a few problems with this:
1) Non English speakers. Ignoring them or telling them to learn English is not a solution.
2) Not everyone is here to trade.
3) If this was the first time I have heard of Bitcoin, I am not going to spend 15 minutes or so doing a reading comprehension test.
Do some A/B testing - I would be very surprised if you don't cut userbase growth by at least 80%.
Points 1 and 2 and 3: You do raise valid points. perhaps a drop down box with language select before the test initiates. i realize not everyone is here to trade, but at the very least there should be a disclaimer in bold red letters about the prevalence of scammers on the board, with a button to opt out of the test.
A/B testing? i'm not familiar with that, but supposing there is an opt out of the test, do you still think it would curb the growth rate of the member base?
If some newbs can't be bothered to read pages upon pages of posts reporting scam and then ask to get in on it, they aren't going to do the test if they can opt-out, are they?!