It's an irregular plural. There's probably some reason for it from old Swedish, but in modern Swedish, that noun is just an exception.
In German it is irregular, too: one book, many books is „ein Buch, viele Bücher“ [aı̯n buːχ fiːlə bʏçɐ]. This method of plural is rather common compared to Swedish, so you are lucky not to learn German. :D
I want to learn German after proficiency is Swedish so I've got a lot to look forward to then ;)
Like berniebud said, it's an exception. A small handful of nouns change their vowel in the plural. Lundgren8 wrote a post about them in the forum, scroll though it and you should be able to find it. :)
Sorry to try to clarify a similar point, but I think mine is slightly different. Can this plural be classified into both the "one syllable" en words as well as the irregular plurals at the same time seeing as though it acquires the -er suffix pertaining to one syllable "en words" while it also changes the main vowel (and a "c" is somehow added)?
Maybe it's redundant and should only be called an irregular plural. Thank you for all your help.
Yeah, there are few irregulars that also get their consonant doubled, böcker has both this and a vowel change. There are a couple that only get their consonant doubled like get → getter and nöt → nötter.
I think they do not give credit if your typo spells another word that has a meaning.
The audio is strange. My Swedish best friend agrees. It sounds more like "becker" as though it uses ä instead of ö.