If these gold coins are minted by that country's mint than yes, they are legal tender in that country at their face-value. But this is still a foreign currency in other jurisdictions, so I doubt it strongly that you could officially pay taxes directly with them anywhere in the world except a country of origin...
Only for the face value portion of the exchange. The commodity value is taxable separately.
That was exactly my point. Is it really possible to pay taxes
directly (i.e. bypassing banks and that kind of things) with gold and silver coins in the USA at their market price?
No. If you don't pay the commodity portion of the tax due, you will go to prison and/or pay hefty fines. There are cases already.
Do you mean to say that if you pay a tax with gold coins at their face-value just like you would do with paper dollars (this is my point, and I specifically mentioned that), I will have to pay additional taxes for the income which I might but didn't actually receive?
Yes.
You spent or received the coin which has a commodity value above and beyond its very low face value, e.g. gold 1oz US Eagles have a $50 face value yet are worth $1300.
http://www.reviewjournal.com/news/employers-gold-silver-payroll-standard-may-bring-hard-timehttp://www.rapidtrends.com/robert-kahre-vs-the-irs-and-doj/http://www.dailypaul.com/210328/can-i-accept-payments-in-gold-report-face-value-as-incomeIt seems that you don't understand what I mean. Your examples only look relevant to my point, though in fact they are quite the opposite of what I mean. If you pay taxes with gold coins at their face value instead of paper dollars (i.e. taxes total being equal coins face value total), you effectively end up paying more than you would pay if you previously sold your coins at their market price and paid the original tax plus the tax due to the commodity value of your coins. How can you possibly be charged for tax evasion if you end up paying more than needed?
I'm not talking here about accepting payments in gold coins, then reporting face value as income