A big restriction in Magento is that it is not possible to use store view codes multiple times for different stores / websites.
For example this should be possible:
www.store1.com/en
www.store1.com/de
www.store1.com/nl
www.store2.com/en
www.store2.com/de
www.store2.com/nl
www.store3.com/en
www.store3.com/de
www.store3.com/nl
But this is not possible, because the store view code must be unique.
Now we have to do something like this:
www.store1.com/en
www.store1.com/de
www.store1.com/nl
www.store2.com/eng
www.store2.com/deu
www.store2.com/nld
www.store3.com/l_en
www.store3.com/l_de
www.store3.com/l_nl
And this just doesn't make sense.
It would be nice to have the possibility to use store view codes across different websites / stores. Or to rewrite the storeview codes on the frontend, something like this:
code - rewrite to
eng - en
fra - fr
deu - fr
english - en
french - fr
german - de