Malaki ang tuwa ng kaibigan.

Because predicate-first word order is very common in Filipino.

In Malaki ang tuwa ng kaibigan, the predicate is malaki (big / great), and the topic is ang tuwa ng kaibigan (the friend’s joy).

So the structure is roughly:

• Malaki = predicate
• ang tuwa ng kaibigan = topic

A more English-like order is also possible:

• Ang tuwa ng kaibigan ay malaki.

That version is grammatical, but it can sound more formal or literary.

Ang marks the topic of the sentence.

Here, ang marks tuwa:

• ang tuwa = the joy

Then ng kaibigan attaches to it and tells whose joy it is:

• ang tuwa ng kaibigan = the friend’s joy

English does not have a direct equivalent of ang, so learners often think of it as a marker that highlights the main noun phrase being talked about.

Here, ng marks a possessor.

So:

• tuwa ng kaibigan = joy of the friend / the friend’s joy

This is a very common pattern in Filipino:

• bahay ng babae = the woman’s house
• kotse ng guro = the teacher’s car
• tuwa ng kaibigan = the friend’s joy

So in this sentence, ng kaibigan tells you who owns or feels the joy.

Yes, literally malaki means big or large, but Filipino often uses it figuratively.

So malaki ang tuwa means something like:

• the joy is great
• the joy is intense
• there is great happiness

This is natural usage. English also does something similar with expressions like great joy.

Because tuwa and masaya are not the same kind of word.

• tuwa = joy / delight (a noun)
• masaya = happy (an adjective)

So:

• Malaki ang tuwa ng kaibigan. = The friend’s joy is great.
• Masaya ang kaibigan. = The friend is happy.

The first sentence focuses on the amount or intensity of joy. The second simply describes the friend as happy.

By itself, kaibigan is normally understood as singular unless context suggests otherwise.

If you want to clearly say friends, you usually use mga:

• kaibigan = friend
• mga kaibigan = friends

So:

• Malaki ang tuwa ng kaibigan. = usually The friend’s joy is great.
• Malaki ang tuwa ng mga kaibigan. = The friends’ joy is great.

By itself, kaibigan just means friend.

It does not automatically mean my friend or your friend. If you want to specify that, you add a pronoun:

• kaibigan ko = my friend
• kaibigan mo = your friend
• kaibigan niya = his/her friend

So ng kaibigan in this sentence just means of the friend, unless the broader context tells you whose friend it is.

Yes, in many contexts that is a natural English translation, even though it is not a word-for-word translation.

Literally, the sentence talks about the friend’s joy being great. But in natural English, that often becomes:

• The friend is very happy.
• The friend is overjoyed.

So the literal structure and the natural meaning are slightly different, and that is normal.

Yes, it is grammatical and understandable, but it can sound a little formal, descriptive, or literary depending on context.

In casual speech, Filipinos might more often say:

• Masayang-masaya ang kaibigan. = The friend is very happy.
• Tuwang-tuwa ang kaibigan. = The friend is very delighted.

So Malaki ang tuwa ng kaibigan is correct, but it is not always the most conversational choice.

Yes. That is also grammatical.

Compare the two:

• Malaki ang tuwa ng kaibigan.
• Ang tuwa ng kaibigan ay malaki.

Both mean essentially the same thing. The difference is mainly in style:

• Malaki ang tuwa ng kaibigan. = more typical predicate-first Filipino
• Ang tuwa ng kaibigan ay malaki. = more formal, sometimes more emphatic or literary

Learners should get used to the first pattern, because predicate-first order is very common in Filipino.