Assimilation doesn't really take much in the way of active policy. As long as there aren't active barriers, people assimilate. None of the parents of the second or third generation asians and latinos I know in the US were met with assimilationist policies but their kids grew up very american. German isn't the easiest language to learn but English is also pretty complicated.
You'd be surprised. Here in the Netherlands, we are having great trouble with assimilation. In the 1950s-1960s our companies hauled in a lot of immigrants from Turkey and Morocco, to work in Dutch industries.
Nowadays, their grandchildren are still not assimilated, at all (except a small minority).
Turkish people have their Turkish supermarkets, Turkish coffee houses, Turkish mosques, and Moroccans have theirs. They keep within their own little circle. They speak Turkish and Moroccan, even when in the company of Dutch people who cannot understand that. If you ask Moroccan or Turkish youth for their nationality, they'll say they're Moroccan, and Turkish, even though their parents, and they themselves were born and raised in the Netherlands.
It's completely opposite of assimilation in America. Most immigrant children in the States, indeed, will proudly say "I am an American".
Good luck trying to find an immigrant (grand)child in the Netherlands (or many other European countries for that matter) that will proudly say "I am Dutch".
Some analist say that the root cause of this is the complete lack of active policy. The grandparents and parents of the current 3d generation immigrant children never got state sponsored Dutch language lessons, or have any social worker come by and see if they can help with fitting in into their new country. They were never encouraged to assimilate.
Other analists say it's a muslim thing, in that a muslim is not allowed to get too involved in political or social activities that do not belong to muslim religion. (Because that would be giving in to fitna - temptation)
Again some other analists say it's latent European xenophobia, where we Europeans subconsciously keep discrimination everyone who is not from our own country, and thus throw up barriers preventing assimilation.