Learn Hardcore Icelandic: Við ákveðum að fara í garðinn á morgun.

Because Icelandic commonly uses the present tense to talk about decisions and plans that affect the future. In this sentence, the deciding happens now (present), and the going happens tomorrow (future), which is made clear by á morgun. Icelandic often uses present + a time expression instead of a separate future tense.

What person/number is ákveðum, and how does ákveða conjugate in the present?

Ákveðum is 1st person plural present (we decide). Present tense of ákveða:

ég ákveð
þú ákveður
hann/hún/það ákveður
við ákveðum
þið ákveðið
þeir/þær/þau ákveða

Could I say a plain future like “We will go to the park tomorrow” instead?

Yes. Two common ways:

Við munum fara í garðinn á morgun. (will go; neutral future)
Við ætlum að fara í garðinn á morgun. (are going to; intention/plan) Your sentence with ákveða highlights the act of deciding.

Do I need að before fara, or can I drop it?

You need að here. After ákveða (decide), Icelandic uses að + infinitive: ákveða að fara. You do NOT use að after modal-like verbs such as vilja (want), geta (can), mega (may), skulu (shall), munu (will): e.g., við viljum fara, við getum farað? (careful: correct is við getum farið, since the infinitive is fara and the supine after geta is farið in periphrastic constructions). The key point: after ákveða, keep að.

Why is it í garðinn and not í garðinum?

Because í governs different cases depending on movement vs. location:

Movement into: accusative → í garðinn (into/to the garden/park)
Location in: dative → í garðinum (in the garden/park) Here you’re going into the park, so accusative garðinn is used.

What’s the -inn ending in garðinn?

That’s the definite article (the), which is suffixed in Icelandic. The noun is garður (a garden/park); accusative singular is garð, and the definite accusative is garðinn (the garden/park). If you wanted “to a park,” you’d say í garð (no article).

Can I say á garðinn instead of í garðinn?

No. With places like gardens/parks, you use í for going into them: í garðinn. The preposition á is used for surfaces/locations like á ströndina (to the beach) or time expressions like á morgun (tomorrow). Á garðinn would mean “onto the garden,” which is not idiomatic.

Where can I put the time expression á morgun? Does word order change the meaning?

Við ákveðum að fara í garðinn á morgun. = We’re deciding to go tomorrow.
Á morgun ákveðum við að fara í garðinn. = Tomorrow we will make the decision to go.
Við ákveðum á morgun að fara í garðinn. = We decide tomorrow to go. Icelandic is verb-second: when you front á morgun, the finite verb ákveðum still stays in the second position.

What’s the difference between í and á in í garðinn vs. á morgun?

Í is generally “in/into” (location vs. movement distinguished by case).
Á is generally “on/onto/at,” but with time expressions it often means “on/at” in the sense of English “tomorrow, on Monday,” etc. Á morgun is a set phrase meaning “tomorrow.”

Why is the subject Við and not Okkur?

Við is nominative plural (“we”) and is used for the subject. Okkur is the oblique form (accusative/dative, “us”) and is used for objects or after certain prepositions. Since “we” is the one deciding, nominative Við is required.

How do I negate the sentence correctly?

Two different meanings:

We decide not to go (the not applies to going): Við ákveðum að fara ekki í garðinn á morgun.
We do not decide to go (the not applies to deciding): Við ákveðum ekki að fara í garðinn á morgun. Placement of ekki determines what is negated.

How do you pronounce the tricky letters and clusters here?

Við ≈ [vɪːð]; ð is like the th in English “this.”
á is a single letter pronounced [au], like the vowel in “cow.”
í is [iː], like “ee” in “see.”
garðinn ≈ [ˈkarðɪn] in careful speech; initial g is often devoiced to a [k]-like sound, ð is “this”-th.
morgun ≈ [ˈmɔrɣʏn]; the rg cluster is often [rɣ] (a voiced fricative). Putting it together (approximate): [vɪːð ˈaukʰvɛːðʏm aːð ˈfaːra iː ˈkarðɪn au ˈmɔrɣʏn].

Is á an accent mark over a, or a different letter?

It’s a different letter in Icelandic (the alphabet includes á, é, í, ó, ú, ý, æ, ö). Á is pronounced [au], not just a stressed “a.” Stress in Icelandic is almost always on the first syllable of a word.

Could I say “in the park tomorrow” instead of “to the park tomorrow”?

Yes, but that changes the meaning. If you want to be in the park (location), use dative:

“We decide to be in the park tomorrow”: Við ákveðum að vera í garðinum á morgun. Your original has movement into the park: að fara í garðinn.

Does garður always mean “park”?

Not always. Garður can mean “garden,” “yard,” or “park,” depending on context. If you specifically mean a public park, you can say almenningsgarður. In everyday speech, garður is often clear from context.

How would I say “We are deciding right now to go to the park tomorrow”?

Use the progressive-like construction vera að:

Við erum að ákveða að fara í garðinn á morgun. This emphasizes the ongoing act of deciding at this moment.