Merkel's epic looking at the glass half empty. Multiculturalism hasn't failed, it's the fact that without the requirement of assimmulation, it's harder for it to work...
America only has recently had it's problem due to certain Hispanic populations who are very nationalistic, who don't want to speak English and want everybody else to speak Spanish. Coupled with the fact that Corps want to make money, so they put things in Spanish, under the guise of helping them, but what it is for is get their money. This creates a system in which their are pockets of Latinos who are isolated from society at large, and when they need help, cannot communicate.
Without he basic requirement of intergration within a society, whether it be German or American shit will hit the fan. Unfortunately, you have to lose a little to gain a lot.