In English (and similarly Swedish), plurals normally take no indefinite articles. (There is actually an indefinite plural article in Swedish, which is used in some very specific circumstances, e.g. expressing astonishment*.)
Now, we can imagine a language where indefinite articles also appear for plurals more regularly.
It seems common for languages with indefinite articles to permit omission of these articles in some contexts, e.g. "I like coffee". In English, the context is nearly exclusively mass nouns, whereas in Swedish it is more 'open', with e.g. nouns after some prepositions preferring to be without articles, complements of the copula often being without articles, and a variety of other contexts which are a bit difficult to catch in a simple description. (I intend to write a description of this at some point.)
So, here's the idea for a detail in a language:
- Plural articles, both definite and indefinite.
- Contexts where the articles are not used.
- For each noun, there is a lexical preference for which number to use when articleless.
- Maybe, just maybe, there is also a preference based on verb and syntactic position, but these preferences interact in some way.
* The plural indefinite article is simply "one" with a plural marker: 'ena'. Examples of expressing astonishment:
det var allt ena dyra mackor
that was all-(neut) a-s expensive-s sandwiches
"ena" is never mandatory, afaict.
'Det var allt' is a set expression also introducing a mildly astonished statement about something.