POST GRADING:

…or even like this: “…Anwendungserlass des Bundesfinanzministeriums zur Abgabenordnung (AEAO) {TRANSLATOR'S NOTE}…”

The American IRS refers to it as the “administrative regulations governing the application of the German Tax Code”—see No. 3 (i) of the “Attachment for Germany” (cf. http://www.irs.gov/businesses/international/article/0,,id=15... ). I'm pretty sure that they know what they're talking about.

As you already know, however, the Bundesverfassungsgericht {Germany's Federal Constitutional Court} has it translated as “Tax Code Application Decree” (see http://www.bundesverfassungsgericht.de/entscheidungen/ls2004... = the reference Bernhard provided). They are sure to know what they are talking about.

Furthermore, the European Union translates this as “decree concerning the implementation of the internal revenue code” (see http://europa.eu.int/comm/secretariat_general/services_gener... ). That may be where your translator got the term (if I understood you correctly, you take it that you are proofreading a translation). Either way, you'd think that they know what they are talking about.

Oh, but there's more: The Faculty of Law at the Central University of calls it “regulations interpreting the AO” (see http://iccsl.org/pubs/CEUNGOLawReader.doc ).

Finally, and you've really got to wonder about this one, the BaFin {Germany's Federal Financial Supervisory Authority} calls it “application order to the Tax Code” (!). Well, actually their translator(s) called it that (see http://www.bafin.de/verlautbarungen/gwg34_en.htm ). They—I'm sure—know what they are talking about.

Unfortunately, I couldn't find anything on the website of the ministry itself.

I think it's important to use the actual name, because if the reader wants to check the source, they're going to have trouble finding a law named the way you (or some other translator) has named it.
;-)