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Well, most certainly Google would consider that to be cloaking on the tumblr subdomain.  I'm not sure that the algorithm would spot this and find it to be a problem, but if I were a Google spam engineer, and asked to look at this, it would be very hard to convince me that it wasn't set up deliberately to build traffic to your site.  I would disavow that tumblr subdomain (the subdomain only, e.g. keywordxxx.tumblr.com, DO NOT disavow tumblr.com!).

Hi there, In order to increase your rankings in German speaking search results it's recommended that you: Use the rel="alternate" hreflang="de" tag, as specified here by Google in order to inform them that this content is in German and targeted to these users. Build links from specific German speaking websites, from blogs, communities, forums, news sites, etc. specially those hosted in German IPs and with German  (.DE) or Swiss (.CH) ccTLDs Since I understand that you're using a .com domain to rank for all of the German speaking countries with the same content, both Germany and Switzerland and not specifically targeted to a specific country (so your site is language, not country targeted) in this case you're not able to geotarget it in Google Webmaster Tools which would be also an additional possibility if you had for example, a specific German version targeting Germany with: yourdomain.com/de/ or targeting to Switzerland with: yourdomain.com/ch/, nonetheless, if at some point you are, is important that you also know of this setting. Moreover, if you switch towards a country targeted domain structure, instead of using a generic domain such .com the best is to switch over a .de targeting Germany and .ch targeting Switzerland. These additional signals should help!