"So Germany doing very well selling cars"
Should Germany set BMW, Mercedes and Volkswagen Group tax rate at 0.005% as well? Would PSA, FCA (which anyway moved to London and Amsterdam to pay less taxes) & C. love that?
Frankly, German cars are not cheap at all - they sell well not for the price, often despite the price (more or less like the iPhone...)
The exchanges rates were fixed well before the Euro. Germany could not undervalue its one much, because Germany still relies on a lot of import of raw materials for its industries. And it would have crippled citizens purchasing power. It's not China.
It's only competing countries that would have liked to see Germany industries put at a disadvantage with lower exchange rates for the Mark and higher for their own currencies - the good, old practice of devaluation to sustain bad companies unable to compete but paying their workers less, while stashing precious currency abroad.
EU rules forbid state aids but in exceptional circumstances, and Ireland violated that.