> It’s generally illegal in most countries to use another country’s passport within the country your passport is from. It's not generally illegal. Some countri

> It’s generally illegal in most countries to use another country’s passport within the country your passport is from. It's not generally illegal. Some countries have that requirement but those are generally countries that are particularly strict (e.g. you mentioned Germany and Argentina but they're both countries famous for unusually strict nationality laws; Germany generally strips people of their nationality if they acquire a foreign nationality, Argentina on the other side makes it impossible to renounce your citizenship at all).