Following these instructions[0] I need to append the l -deu argument (language flag). I tried appending it quoted to the command ocrmypdf below. It fails (output.pdf missing).
parallel --tag -j 2 ocrmypdf '-l deu' '{}' 'output/{}' ::: *.pdf
The original command runs without hassle:
parallel --tag -j 2 ocrmypdf '{}' 'output/{}' ::: *.pdf
Looking at other answers e.g. [1] didn't help