If you have a proof of residency in Namibia you can buy a Eurail pass. Otherwise you must buy an Interrail pass and then you can only use 2 travel days in Germany.

As above: NUR WENN mann deutlich beweisen kann dass mann irgendwo anders als im land des passes wohnt geht das. Es soll gerade für DE dann selbstverstdl sein das mi EUrail auch nur lästige extra Prüfungen usw in DE wo mann Regeln usw mal gerne sehr ernst nimmt zu erwarten sind.

Bin selber mit 3-Mon InRail im Herbst (davon etwa 75 T verreist in 17 Länder) bloss 2x weiter nach ID gefragt-einmal davon in was sehr deutlich eine Instruktion von Meister zur Azubi war.

The rule is simple - if you have proof of residency in a non-european country (some form of formal document), normally something showing over 6 months residency, but not a specific requirement, then a Eurail pass is fine.

Inspectors are not going to be overly bothered with the detail, simply that it displays your eligibility for Eurail rather than Interrail.

You can though travel with your German passport as normal as that is your citizenship document for all other purposes. 

If a user has dual passports you do need to use the same passport in and out of Europe, but that in no way affects your use of a pass.

Thanks everyone. Your answers were very helpful.