Kakak perempuan saya menyimpan seragam kerja di loker karena dia masuk shift pagi.

Kakak by itself means older sibling and does not tell you whether the sibling is male or female.
If you want to be specific, you can add:

• kakak perempuan = older sister
• kakak laki-laki = older brother

So kakak perempuan saya means my older sister.

In everyday conversation, Indonesians often just say kakak saya if the gender is already clear from context.

In Indonesian, possessors usually come after the noun.

So:

• kakak perempuan saya = my older sister
• rumah saya = my house
• buku dia = his/her book

This is different from English, where my comes before the noun.

Menyimpan usually means to store, to keep, or to put something away.

In this sentence, it suggests that the older sister is putting the work uniform in the locker for keeping/storage, not just placing it somewhere casually.

Compare:

• menyimpan = store/keep/put away
• meletakkan = place/put down
• menaruh = put/place

So menyimpan seragam kerja di loker sounds like keeping the work uniform in a locker, which fits the context well.

The base word is simpan = keep/store.

With the prefix meN-, it becomes menyimpan.

This is part of a common Indonesian verb-forming pattern:

• simpan → menyimpan
• baca → membaca
• tulis → menulis

For learners, the most useful thing is to recognize that meN- often makes an active verb. So menyimpan means to store/keep as an action being done by the subject.

It literally means work uniform.

• seragam = uniform
• kerja = work

Indonesian often puts nouns together like this, where the second word describes the first:

• seragam kerja = work uniform
• jam kerja = working hours
• baju tidur = sleepwear / pajamas

So there is no need for a word like for in Indonesian here.

Because di here is a preposition meaning in / at / on, and prepositions are written separately from the following word.

• di loker = in the locker
• di rumah = at home
• di kantor = at the office

This is different from di- as a verb prefix, which is written together:

• disimpan = is stored
• ditulis = is written

So:

• di loker = correct
• diloker = incorrect in this sentence

Loker is a commonly used Indonesian word meaning locker. It is borrowed from English, but it is fully natural in modern Indonesian.

You will hear it often in workplaces, schools, gyms, and hospitals.

Example:

• Saya taruh tas di loker. = I put my bag in the locker.

Karena means because.

It introduces the reason:

• Kakak perempuan saya menyimpan seragam kerja di loker = My older sister stores her work uniform in the locker
• karena dia masuk shift pagi = because she works the morning shift / starts the morning shift

So karena connects the action with its reason.

Literally, masuk means enter or go in, but in many real-life contexts it also means to start work, to be on duty, or to have a scheduled shift/class.

So dia masuk shift pagi means something like:

• she is on the morning shift
• she starts the morning shift
• she works the morning shift

This is a very natural Indonesian expression. Similar uses include:

• Saya masuk jam 8. = I start work at 8.
• Besok dia masuk pagi. = Tomorrow she has the morning shift / works in the morning.

Shift is a widely used loanword in Indonesian, especially in workplace contexts.

So:

• shift pagi = morning shift
• shift malam = night shift

You may also hear more formal or less borrowed alternatives in some contexts, but shift is extremely common and natural in everyday Indonesian.

Dia means he or she. Indonesian does not mark gender in this pronoun.

So dia can mean either:

• he
• she

In this sentence, from context, it refers to the older sister, so it means she.

Indonesian can sometimes omit subjects if they are obvious from context, but keeping dia makes the sentence clearer:

• ...karena dia masuk shift pagi = because she is on the morning shift

If you removed dia, the sentence might still be understandable in conversation, but it would be less explicit.

No, Indonesian does not use articles in the same way English does.

So:

• seragam kerja can mean a work uniform, the work uniform, or simply work uniform
• loker can mean a locker or the locker

The exact meaning depends on context.

That is why the sentence does not need words corresponding to a or the.

Yes. Indonesian allows flexibility here.

The original sentence:

• Kakak perempuan saya menyimpan seragam kerja di loker karena dia masuk shift pagi.

You could also say:

• Karena dia masuk shift pagi, kakak perempuan saya menyimpan seragam kerja di loker.

Both mean essentially the same thing: Because she works the morning shift, my older sister keeps her work uniform in the locker.

The original version sounds very natural and straightforward.

It is mostly neutral everyday Indonesian.

Words like saya, menyimpan, and karena are standard and natural.
The use of shift and loker is also normal in modern everyday speech.

In very casual conversation, someone might choose simpler or more spoken-style wording, but the sentence as given is perfectly normal and clear.