Learn Hardcore Indonesian: Saya juga berdoa agar pernikahan mereka bahagia dan hubungan mereka selalu kuat. - I also pray that their marriage will be happy and that their relationship will always be strong.

Agar introduces the content of a hope, wish, or purpose, roughly like “so that / in order that / that” in English.
In this sentence, berdoa agar… means “to pray that…”.

agar and supaya are very close in meaning and often interchangeable; agar sounds a bit more formal or written, supaya a bit more colloquial.
bahwa = “that” for reporting facts (after verbs like mengatakan “to say”, menyadari “to realize”). With berdoa, native speakers normally choose agar/supaya, not bahwa, because praying is expressing a wish, not simply reporting information.

Why is there no word like “is/are” (a linking verb) between pernikahan mereka and bahagia?

Indonesian usually does not use a separate “to be” verb before adjectives.
So:

pernikahan mereka bahagia literally = “their marriage happy”, which functions as a full clause: “their marriage is happy”.
You do not say ✗ pernikahan mereka adalah bahagia. Adalah is used mainly between two nouns (e.g. Dia adalah guru “He is a teacher”) or in formal definitions, not before ordinary adjectives like bahagia, kuat, tinggi, etc.

Could we say “Saya berdoa untuk pernikahan mereka…” instead of “Saya berdoa agar pernikahan mereka…”? What’s the difference?

Yes, but the structure changes slightly:

Saya berdoa agar pernikahan mereka bahagia…
→ agar must be followed by a clause (subject + predicate). Here the clause is pernikahan mereka bahagia.
Saya berdoa untuk pernikahan mereka.
→ untuk is followed by a noun phrase (pernikahan mereka). This means “I pray for their marriage” in a more general sense, without explicitly stating what you want to happen.

You can also combine them:
Saya berdoa untuk pernikahan mereka, agar pernikahan mereka bahagia dan hubungan mereka selalu kuat.

Why isn’t there any future marker like akan? English says “will be happy / will always be strong”.

Indonesian normally does not have to mark future tense explicitly. The context (praying about their marriage) already implies it’s about the present and future.

pernikahan mereka bahagia can mean “their marriage is happy” or “their marriage will be happy”, depending on context.
You can add akan: agar pernikahan mereka akan bahagia and hubungan mereka akan selalu kuat, but many speakers find akan here a bit unnecessary or heavy. The original sentence sounds more natural and still covers the idea of future well-being.

Why is bahagia used with pernikahan, not senang or gembira?

All three relate to positive feelings, but their usage differs:

bahagia = happy in a deeper, more lasting way; often used for life situations or relationships: pernikahan bahagia (a happy marriage), keluarga yang bahagia (a happy family).
senang = glad / pleased; often about momentary feelings: Saya senang (I’m pleased / happy right now).
gembira = joyful, cheerful; often about visible joy or excitement: Anak-anak tampak gembira (The children look very happy/excited).

So pernikahan mereka bahagia sounds natural and idiomatic for “their marriage is (or will be) happy.”

What exactly does hubungan mean here? Is it only romantic?

Hubungan literally means “relationship / connection” and comes from the root hubung (“to connect, to relate”). It is very general:

hubungan mereka can mean their romantic relationship (as a couple), which is the most likely reading here.
But hubungan is also used for non-romantic contexts: hubungan kerja (work relationship), hubungan keluarga (family relationship), hubungan internasional (international relations).

In this sentence, combined with pernikahan, it clearly refers to the couple’s personal/romantic relationship.

Why selalu kuat and not tetap kuat? Do they mean different things?

Both are possible but the nuance is slightly different:

selalu kuat = “always strong” → focuses on continuous strength over time, without specifying any threat or change.
tetap kuat = “remain/stay strong” → emphasizes not changing or not weakening, often in the face of difficulties.

If you say hubungan mereka selalu kuat, you’re wishing that their relationship will constantly be strong.
If you say hubungan mereka tetap kuat, you’re wishing that their relationship will stay strong even when challenged. Both sound natural as a blessing.

Can juga be placed in another position, like “Saya berdoa juga agar…”? Does the meaning change?

Yes, juga is somewhat flexible:

Saya juga berdoa agar… – the most common; “I also pray that…”. Emphasis slightly on “I also…” (in addition to doing other things, or in addition to other people).
Saya berdoa juga agar… – also possible; often read as “I pray also that…”, as if you’re adding an extra prayer on top of some earlier one.
Saya berdoa agar… juga – here juga usually attaches to what comes before it; in this sentence, it could sound awkward or ambiguous.

The original placement (Saya juga berdoa…) is the clearest and most natural version in most contexts.

Could we use Aku instead of Saya here? What’s the difference in tone?

Yes, grammatically you can:

Saya – neutral, polite, standard; used in most formal or semi-formal situations, with people you don’t know well, or in writing.
Aku – informal, more intimate; used with friends, family, or people of the same age/close relationship.

So:

Saya juga berdoa… sounds neutral/polite.
Aku juga berdoa… feels more personal or casual, like you’re talking to close friends or writing something intimate.

The rest of the sentence doesn’t need to change if you switch saya ↔ aku.

What are the parts inside pernikahan, hubungan, and berdoa? How are they formed?

These are common noun/verb formations using affixes:

nikah (root) = to marry
→ pernikahan = per- + nikah + -an → “marriage” (the noun, the event/state)
hubung (root) = to connect, to relate
→ hubungan = hubung + -an → “relationship / connection”
doa (root) = prayer
→ berdoa = ber- + doa → “to pray”

Knowing these patterns helps you guess meanings of many other words in Indonesian with per- -an, -an, and ber-.