Someone I know is a dual citizen of Sweden and Russia, holding a Swedish ID card and Russian internal passport, but neither a Swedish passport nor Russian external passport.
She's planning to travel overland Sweden - Finland - Russia - Georgia - Armenia.
Georgia accepts Swedish IDs while Armenia accepts Russian internal passports. And obviously entering Russia on an internal passport shouldn't be a problem, as it proves she's Russian.
The problem is: I've heard that Russia doesn't let you exit on an internal passport other than to countries accepting them for entry, which the next country, Georgia, doesn't.
Is this true? What if she explains that she's a dual national and using another document for Georgia?
UPDATE: OK, so I spoke to the concerned person as you had some questions. Her father registered her birth with the embassy in Stockholm and got her an international passport (she's had two, one between 2004-2009 and one between 2009-2014), with which her family visited Russia on several occasions, most recently in 2012. In 2013-2014, she spent an exchange year in St Petersburg, during which she got the internal passport, which is valid until 2019. Shortly after returning to Sweden, her international passport expired and she hasn't got a new one since.
UPDATE 2: I finally convinced her to get an (old template) Russian external passport. So apparently she'll use all three documents during the trip: Swedish ID at Schengen and Georgian borders; international Russian passport at the Russian border, and Russian internal passport at the Armenian border.