Viadeo is worst. I have closed my account like three of four times ... they keep reopening it and spamming me. If I receive another mail from them, I will complain to the CNIL.
Xing is made by a Perl company in Germany, specifically Hamburg. Having had some experience with other web-related companies, most german software is written with german content first, and little thought spent on localization, since serving an audience outside of germany is risky in that it means a lot of the company (support, etc.) has to be duplicated first, and it might end up having little draw. On the flipside, most Perl web frameworks are build with only one language in mind, English. Adding localization is extremely easy if you start out with it in mind, and i've actually been working on tools to ease that process, but after the fact it's a massive investment.
Due to all these factors the cost is simply too high for most german companies to even try.