"The turtle eats bread."
Translation:Skilpadda spiser brød.
That's not how it's formed. "-an" is not a legal form for any noun in bokmål as far as I know. "En skilpadde - skilpadden" or "Ei skilpadde - skilpadda".
The article "en" just gets added to the end, the article "ei" gets added as an -a. If it as a neuter noun the article "et" gets added to the end.