No conversion to dollar necessary. An American citizen say lives on the US Canada border and has a job just across the line and gets paid in Canadian dollars they are still expected to pay income tax. If an American citizen lives and works in France for a decade they are expected to file income taxes in the US every year. Income tax is just that, tax on income it applies to every citizen of the US no matter where they live or what currency they get paid in. BTC is no different.
I am no expert on american taxes (eh, IANEOAT?) but I believe there is a treaty between France and USA preventing double taxation. You might or might not be forced to file the papers but if you're already paying taxes from the income in France (as would be the case - since the employer would just deduct it) you wouldn't have to pay the US taxes.
