To the best of my knowledge, eBay doesn't have its own translation facility and, even if it did, I can't see how a page from their site could add an option onto the right-click menu of your browser.
That means that the translation facility must have either been provided by your browser re-routing the page via an online translation service, or through an add-on (such as a toolbar) doing the same thing.
I'm not sure which browsers or toolbars can do this but you need to consider what's changed on your PC recently. For example have you uninstalled a toolbar provided by a search engine? If so, try reinstalling it.
If that doesn't help you solve the problem, you can still translate eBay's German website. Simply type in www.ebay.de in the 'Translate a web page' box, on the Babelfish site. Select 'German to English' and click 'Translate'. eBay's home page, and all links from it, will appear in translation:
http://babelfish.altavista.com
Chris