You might be able to get the engineer to agree that the European steel you want to use can be considered equivalent to a particular U.S. grade of steel.  D1.1 explicitly allows this for "auxiliary" attachments in clause 3.4, but I'm assuming you're talking about primary members.

More likely, you'll have to run a qualification test per 4.7.3 and Table 4.9.  That's what I'd make you do if it were my project.

Hg

ISO Standard TR 20173 - 2005 gives an approximate equivalence of American, European and Japanese steels. That standard will tell you what's the American steel equivalent to EN 10210. However, these equivalences are only approximate, so the fact that your welding procedures for EN 10210 have been approved, it doesn't mean that they are authomatically approved for its American equivalent. I agree with HgTX's suggestion, which I consider sound and valid, but I'll give you another one, so you can choose the one that is more convenient to you.
Check on the ISO standard which is the American equivalent to EN 10210. Once the material has arrived from Europe and is in your possession, have a qualified lab (there are quite a few here in Brazil, so there must be much more in the USA) run the tests required by the applicable American standard (ASTM? SAE?) as for example chemical analysis, tensile stress, impact etc.
If the tests results follow the requirements of the applicable American standard, then there's no doubdt: the European material can be classified as pertaining to the applicable American standard because it satisfies its requirements.
A complete chemical analysis of steel in a qualified Brazilian lab cost about 20 (twenty) US dollars.
Giovanni S. Crisi
Sao Paulo - Brazil