Sebelum berangkat, Ibu memeriksa resleting jaket adik saya yang masih terbuka.

Sebelum berangkat means before leaving or before setting off. It gives the time/background for the main action.

Indonesian often puts this kind of time phrase at the start of the sentence, followed by a comma:

Sebelum berangkat, Ibu memeriksa ...
= Before leaving, Mother checked ...

You could also move it later in some contexts, but starting with it is very natural.

In Indonesian, it is very common to leave out a subject when it is understood from context.

So sebelum berangkat literally looks like before departing/leaving, without saying exactly who is leaving. English usually wants a subject, but Indonesian often does not.

In this sentence, the most likely meaning is simply before leaving in a general contextual sense. Depending on context, it could refer to the family, the mother, or the person being discussed.

Ibu literally means mother or mom, but it is also a polite title for an adult woman, similar to Mrs., Ms., or ma’am depending on context.

In this sentence, because of the family context with adik saya (my younger sibling), Ibu most naturally means Mother/Mom.

Also, when used like a name or title, Ibu is often capitalized.

Memeriksa means to check, to inspect, or to examine.

It comes from the root periksa. The prefix meN- turns it into an active verb:

• periksa = inspect/check
• memeriksa = to check / checked

So Ibu memeriksa resleting... means Mother checked the zipper...

In standard Indonesian, the meN- form is commonly used for active verbs in normal declarative sentences.

So:

• Ibu memeriksa resleting = standard, natural written Indonesian
• Ibu periksa resleting = possible in certain informal, conversational, or special contexts, but not the normal standard form here

For learners, a good rule is: when the subject is doing an action in a regular active sentence, the meN- verb is often the expected form.

Resleting means zipper or zip.

It is a loanword, historically from Dutch ritssluiting. Modern Indonesian speakers just treat it as a normal Indonesian noun.

You may also hear rits, which is a shorter and very common way to say zipper.

So these are both possible in everyday Indonesian:

• resleting jaket
• rits jaket

Indonesian usually shows possession by putting the possessed thing first, followed by the owner:

• jaket adik saya = my younger sibling’s jacket
• literally: jacket younger sibling my

There is no need for a word like of.

This structure is very common:

• rumah saya = my house
• buku guru = the teacher’s book
• mobil ayah = father’s car

So jaket adik saya means the jacket belonging to my younger sibling.

Adik means younger sibling, so by itself it does not tell you whether the person is male or female.

So adik saya can mean:

• my younger brother
• my younger sister
• my younger sibling

If the gender matters, Indonesian can add more information, but often it is simply left unspecified.

Yang introduces a phrase that describes the noun before it. In English, it often works like that, which, or who.

Here:

resleting jaket adik saya yang masih terbuka

The phrase yang masih terbuka describes resleting:

• yang = that/which
• masih terbuka = still open

So the meaning is the zipper of my younger sibling’s jacket that was still open.

Grammatically, it most naturally describes resleting (zipper), because that is the noun immediately before yang.

So the intended reading is:

Mother checked my younger sibling’s jacket zipper, which was still open.

That also makes the most sense logically, since a zipper can be open in a very direct way.

Masih means still.

It shows that a situation continues when you might expect it to have changed.

So:

• terbuka = open
• masih terbuka = still open

This suggests that the zipper had not been closed yet.

Buka is the root related to open.
Terbuka is a stative/passive-like form meaning open or in an open state.

In this sentence, we are describing the condition of the zipper, not telling someone to open it.

Compare:

• buka pintu! = open the door!
• pintunya terbuka = the door is open

So yang masih terbuka means which was still open, describing a state.

The sentence can be broken down like this:

• Sebelum berangkat = time expression
• Ibu = subject
• memeriksa = verb
• resleting jaket adik saya = object
• yang masih terbuka = modifier describing the object

So the pattern is roughly:

Time phrase + Subject + Verb + Object + Describing clause

That is a very common and natural structure in Indonesian.

Yes. Even if the basic meaning stays the same, several English translations are possible:

• Before leaving, Mother checked my younger sibling’s jacket zipper, which was still open.
• Before they left, Mom checked the zipper of my younger sibling’s jacket, which was still open.
• Before setting off, Mom checked my younger sibling’s still-open jacket zipper.

The Indonesian sentence itself is natural and straightforward, but English may choose different wording depending on style.