Learn Hardcore Swedish: De gamla tidningarna ligger i garaget.

Yes—Swedish uses “double definiteness” with attributive adjectives. When you have a definite noun with an adjective before it, you add a separate definite article plus the definite ending on the noun:

Without adjective: Tidningarna ligger i garaget. (The newspapers…)
With adjective: De gamla tidningarna ligger i garaget. (The old newspapers…)

This pattern is: den/det/de + adjective + noun-definite-suffix.

Could it be “Dem gamla tidningarna”?

No. In standard writing, the article must be de. Dem is only an object pronoun (“them”) and cannot function as the article before an adjective. Informally, many people write and say dom for both de and dem, but in standard written Swedish this sentence uses de.

Is “de” here a pronoun meaning “they,” or an article meaning “the”?

An article. In De gamla tidningarna, “de” is the plural definite article used with an adjective. If it were the pronoun “they,” it would stand on its own (e.g., De ligger i garaget = “They are in the garage”).

How do you pronounce “de” here?

In everyday Sweden-Swedish, both de and dem are often pronounced “dom,” so you’ll commonly hear: Dom gamla tidningarna…
In careful speech or Finland-Swedish, de sounds like “deh.” Some helpful approximations:
gamla ≈ “GAHM-la”
tidningarna ≈ “TEED-ning-ar-na” (the “rn” often blends into a retroflex sound)
garaget ≈ “ga-RAH-shet” (the “ge” gives a “sh”-like sound)

Why is it “ligger” instead of “är” for “are”?

Swedish frequently uses “posture”/position verbs for location:

ligger (lie) for things lying flat or spread out
står (stand) for things upright
sitter (sit) for people/objects “sitting” You can say Tidningarna är i garaget (neutral “are”), but ligger adds the natural posture nuance for newspapers.

Could I use “står” or “finns” instead?

står fits upright items (bottles, boxes, a vacuum cleaner). For newspapers, use ligger unless they’re stored upright.
finns means “can be found/exists.” Tidningarna finns i garaget is fine if you mean “That’s where they’re located (to be found),” without describing posture.

Why “i garaget” and not “på garaget”?

i = “in/inside” a place: i garaget (in the garage).
på = “on/on top of” or sometimes “at” certain locations: på garaget would mean “on top of the garage (roof).”

Why is it “garaget” (definite)? Could it be “i ett garage”?

Use the definite when both speakers know which garage is meant (e.g., your house’s garage): i garaget. Use the indefinite i ett garage if it’s not a specific one or not known to the listener.

What are the forms of “tidning” here?

Indefinite singular: en tidning (a newspaper)
Indefinite plural: tidningar (newspapers)
Definite plural: tidningarna (the newspapers)

Many common-gender nouns form the plural with -ar and the definite plural with -arna.

Why is the adjective “gamla” and not “gammal” or “gammalt”?

Adjectives agree with gender, number, and definiteness:

Indefinite singular common: en gammal tidning
Indefinite singular neuter: ett gammalt hus
Indefinite plural: gamla tidningar/hus
Definite (with article): den gamla tidningen, det gamla huset, de gamla tidningarna

So with plural definite, you need gamla.

Can I drop “de” and say “Gamla tidningarna ligger i garaget”?

Not in standard Swedish. With an attributive adjective and a definite noun, you need the article: De gamla tidningarna. Exceptions: with possessives or names/genitives you do not use the article or the definite suffix, e.g., mina gamla tidningar (not “mina gamla tidningarna”), Peters gamla tidningar.

How would I say it if I don’t mean specific newspapers?

Use the indefinite plural: Gamla tidningar ligger i garaget = “Old newspapers are in the garage” (some nonspecific old newspapers). With a number: Två gamla tidningar ligger i garaget. Note that you wouldn’t use the definite article or the noun’s definite ending in those cases.

What happens to word order if I start with the place?

Swedish main clauses are V2 (the finite verb is in second position). If you front the place, the verb still comes second:

I garaget ligger de gamla tidningarna.

How do I negate it?

Place inte after the finite verb:

De gamla tidningarna ligger inte i garaget. With fronting:
I garaget ligger inte de gamla tidningarna.

What’s the past tense and perfect of “ligger”?

Present: ligger
Past (preterite): låg — De gamla tidningarna låg i garaget.
Supine (for perfect): legat — De gamla tidningarna har legat i garaget.

What’s the difference between “De gamla tidningarna ligger i garaget” and “Tidningarna ligger i garaget”?

De gamla tidningarna… specifies you’re talking about the old newspapers (not the new ones).
Tidningarna… refers to “the newspapers” without stating they’re old; context would decide which ones you mean.