Licht & Feuer wrote:Not that I dislike this but more and more it seems that the countries just do what they want
In many regards that is true in the EU.

As for those coins, however ... well, the Vatican has always issued Sede Vacante coins, and the monetary agreement with the EU even allows for a higher mintage volume in such years. And yes, Germany and Luxembourg (but also Finland and Portugal, and maybe others) issue two commemorative €2 coins this year.
They can do that because Article 2 of the Commission Recommendation regarding such coins (2003/734/EC), adopted by the Council in late 2003, says that "the number of issues should be limited to one per issuing State per year (...). This limit would not apply to possible commemorative euro circulation coins collectively issued by all euro-area countries". The Treaty of Rome coin is such a "collectively issued" piece, so each member state can issue a second commem ...
Licht & Feuer wrote:I guess the reason is national law, as far as I know many "royal" countries say that their monarch as head of state must appear on all coinage. I think in Belgium and the Netherlands it's the same.
Not quite. In Belgium that is not mandatory (think of the Atomium €2 coin - no Albert there), and the Netherlands actually modified the
muntwet so that on such European issues the head of state does not have to be depicted.
Good news regarding the French contribution by the way: Apparently their €2 Treaty of Rome coin will be minted for circulation too, with a mintage of almost 10 million. So not just for sets ...
Christian