IBKR now offers German government bonds for trading.
Type a country's abbreviation (ie, "MX" for Mexico, "DE" for Germany, "HU" for Hungary, etc) into an empty line in the TWS, press Enter, and choose "Government Fixed Income" from the menu. A list of sovereign bonds will populate.
For information on the bonds offered through IBKR, please visit the Product Listings page of the Interactive Brokers website and select Bonds.