Upvote:6
As the citizen of a country, you have the right to enter that country as long as you have documentary proof that you are a citizen of that country, passport or otherwise. So if you show up at the border waving your certificate, you'll eventually get in, although it may take a while.
The big problem is going to be getting to that border in the first place. Airlines flying into a country are going to insist on a passport or some sort of temporary travel document, a random certificate is not going to cut it.
And you're most likely to have trouble even leaving your home country, since exit immigration is going to want to see your passport: you can't just show them your other-country passport, since that's not going to have a visa and would make you an illegal immigrant. You might be able to argue your way out, but it would be highly unusual to say the least.
Obviously this applies to places primarily reached by air and where border controls are enforced. If you're a new citizen of (say) Finland but decide to keep renewing your (say) Swedish passport, you're not even going to need the citizenship certificate, because there are no border controls between the two and a Swedish passport is completely valid for entering any Schengen country.