Learn Hardcore Indonesian: Rak di perpustakaan penuh buku. - The shelf in the library is full of books.

Indonesian doesn’t need a linking verb before adjectives. Penuh is a stative adjective (“full”) that can function as the predicate by itself, so Rak di perpustakaan penuh buku literally reads “Shelf in library full (of) books.” You would not use adalah here; adalah is typically used before noun predicates (e.g., definitions), not adjectives.

What does di mean in di perpustakaan, and is the spacing important?

di means “at/in” and marks a location: di perpustakaan = “in the library.”
Spacing matters: as a preposition, di is written separately (di perpustakaan). The attached form di- (no space) is a passive verb prefix (e.g., dipenuhi “be filled”). Don’t confuse the two.

Should it be penuh buku or penuh dengan buku?

Both are acceptable:

penuh buku: concise, common in everyday speech.
penuh dengan buku: slightly more explicit/neutral; very common and always safe. Related alternatives:
dipenuhi (oleh) buku-buku: “is filled (by) books,” more formal/passive.
penuh akan tends to collocate with abstract nouns (e.g., penuh akan makna “full of meaning”), not usually with concrete countables like books.

Why doesn’t buku show plural (books)? Do I need buku-buku?

Indonesian nouns don’t change for number. buku can mean “book” or “books,” and in penuh buku the context already implies “books.” You can use:

buku-buku to emphasize plurality.
Quantifiers if needed: banyak buku (many books), beberapa buku (several books).

How do I say “the shelf” vs. “a shelf”?

Indonesian has no articles. Common ways:

“the (that) shelf”: add itu to the noun phrase, e.g., Rak di perpustakaan itu penuh buku (“The shelf in that library is full of books.”)
“this shelf”: Rak di perpustakaan ini penuh buku.
“a shelf / one shelf”: Sebuah rak di perpustakaan penuh buku (you can also say Satu rak… in casual speech).
A previously known/possessed thing can take -nya: di perpustakaannya (“in the/that/his/her library,” depending on context).

Do I need yang as in Rak yang di perpustakaan?

Not here. di perpustakaan is a simple prepositional modifier and doesn’t require yang. Use yang to form a relative clause when you need to pick out or contrast a specific one:

Rak yang di perpustakaan penuh buku = “The shelf that is in the library is full of books” (contrasting with shelves elsewhere). Without such contrast, Rak di perpustakaan penuh buku is more natural.

Can I change the word order?

Yes. All of these are possible, with slight shifts in emphasis:

Rak di perpustakaan penuh buku. (given)
Rak penuh buku di perpustakaan. (focuses on “full of books,” then adds the location)
Di perpustakaan, rak penuh buku. (fronts the location as the topic) All remain grammatical.

How do I say “The shelf in the library is not full of books”?

Use tidak to negate adjectives:

Rak di perpustakaan tidak penuh (dengan) buku. Use bukan only to negate a noun predicate (e.g., Itu bukan rak = “That is not a shelf”), not an adjective like penuh.

Do I need a measure word like buah with rak?

Not unless you are counting or specifying quantity. Examples:

Tiga rak di perpustakaan penuh buku. (Three shelves…)
Sebuah rak di perpustakaan penuh buku. (One/a shelf…) You don’t add buah by default; it’s optional and more common in counting: sebuah rak, tiga buah rak.

How do I make the subject plural, as in “The shelves in the library are full of books”?

Several ways:

Reduplication: Rak-rak di perpustakaan penuh buku.
Quantifiers: Semua rak di perpustakaan penuh buku. (All shelves…)
A number: Dua puluh rak di perpustakaan penuh buku. No verb agreement is needed; the predicate stays the same.

Is rak the right word? What about lemari or rak buku?

rak = shelf/rack (usually open shelving).
rak buku = bookshelf/shelving for books.
lemari = cabinet/wardrobe (enclosed, with doors). Choose based on the furniture: open shelves (rak/rak buku) vs. a closed bookcase (lemari buku).

Could I use ada to talk about existence instead of describing the shelf?

Yes, to state existence you can say:

Di perpustakaan ada rak yang penuh buku. = “In the library, there is a shelf that is full of books.” This shifts the focus from describing a known shelf to asserting that such a shelf exists.