The EU treaties allow each country to have a minimum wage and grant them the ability to enforce it.
pay the same wages
That is not what is happening. Polish companies are not forced to pay the same as German companies, they are just bound to the same rules as German companies are. It prevents them from exploiting their workers. I mean let us be clear here. The minimum wage in Germany is very low. It barely allows for a living. Forcing your qorkers to go below that while they live in Germany is exploitation.
is usually bad for German interests
You keep saying that, but so far you haven't really pointed out those fundamentally different interests.
And as side note, even if Poland had different interests, it could not do a worse job to realize them if they tried. Self-isolation is never a smart move in European politics.
that you could have sorted this
Any ideas how? I mean the basic idea behind the minimum wage is to assure that workers can actually live from the work they are doing without government aid. The only alternative would have been to allow German companies to undercut it and for the state to pay the difference. However this not only would have defeated the purpose of minimum wage, it would also have been illegal state aid. If you look at it ovjectively, this was the only legal and fair solution. Honestly, I dont want to think that the guys working at a local construction site are doing their backbreaking work for like 2€ an hour.