Usisahau kufunga kitasa cha mlango wa nyuma kabla ya kulala.

Usisahau means don’t forget.

It is a negative command addressed to one person. In Swahili, a common way to make a negative command to you (singular) is:

• usi-
  • verb stem

So:

• sahau = forget
• usisahau = don’t forget

If you were speaking to more than one person, you would usually say:

• msisahau = don’t forget (plural)

Kufunga is the infinitive, meaning to close / to fasten / to lock depending on context.

After usisahau, Swahili often uses an infinitive to express the action you should not forget to do:

• Usisahau kufunga... = Don’t forget to lock/close...
• literally: Don’t forget to do the locking/closing...

This is very similar to English don’t forget to...

The verb funga has a range of related meanings, including:

• close
• shut
• fasten
• lock

The exact translation depends on what is being closed or fastened.

In this sentence, because it says kitasa (a latch/lock/bolt), kufunga is best understood as something like:

• to fasten the latch
• to lock
• to secure

So even if the full literal wording mentions the latch, the natural English meaning may simply be lock the back door.

Kitasa means a latch, bolt, or sometimes lock, depending on context.

It refers to the thing that secures the door. So:

• kufunga kitasa = to fasten the latch / to lock it

This word belongs to the ki-/vi- noun class:

• singular: kitasa
• plural: vitasa

The word cha is a connector meaning something like of or belonging to, and it must agree with the noun that comes before it.

Here, the noun before it is kitasa, which is in the ki-/vi- class. For that class, the connector is:

• cha (singular)
• vya (plural)

So:

• kitasa cha mlango = the latch/lock of the door

If the first noun belonged to a different noun class, the connector would change. For example:

• mlango wa nyumba = door of the house

So cha is used because it agrees with kitasa, not with mlango.

Literally, mlango wa nyuma is door of the back/rear.

Swahili often expresses ideas like English compound nouns in a more analytic way, using a connector such as wa. So instead of putting back directly before door, Swahili says something more like:

• mlango = door
• wa nyuma = of the back / rear

Together:

• mlango wa nyuma = back door

The connector wa agrees with mlango.

Nyuma usually refers to back, rear, or behind.

In this phrase, it is not behaving like a simple English-style adjective. Instead, Swahili uses the construction:

• mlango wa nyuma

This is more literally door of the rear/back.

So a useful way to think of nyuma is as a word referring to the back/rear area, rather than as a direct adjective like English back.

Kabla ya kulala means before sleeping or before going to bed.

Breakdown:

• kabla = before
• ya = linker used after kabla
• kulala = to sleep

So:

• kabla ya kulala = before sleeping / before going to sleep

This is a very common pattern in Swahili:

• kabla ya
  • noun or infinitive

Examples:

• kabla ya kazi = before work
• kabla ya kuondoka = before leaving

In standard Swahili, kabla is commonly followed by ya when linking to a noun or infinitive phrase.

So you say:

• kabla ya kulala
• kabla ya chakula
• kabla ya kuja

not normally just:

• kabla kulala

A good rule for learners is:

• memorize kabla ya as a set phrase meaning before

The structure is:

• Usisahau = don’t forget
• kufunga = to lock / fasten
• kitasa cha mlango wa nyuma = the latch/lock of the back door
• kabla ya kulala = before going to sleep

So the sentence builds like this:

• Don’t forget
• to lock
• the latch/lock of the back door
• before going to bed

A very natural English translation is:

• Don’t forget to lock the back door before going to bed.

Yes. That is a good literal translation.

However, in natural English, people would usually say:

• Don’t forget to lock the back door before going to bed.

So there are really two levels here:

• literal: fasten the latch of the back door
• natural English: lock the back door

Both reflect the Swahili sentence well, depending on how literal you want to be.

You would usually change usisahau to msisahau:

• Msisahau kufunga kitasa cha mlango wa nyuma kabla ya kulala.

That means:

• Don’t forget to lock the back door before going to bed.
  when speaking to more than one person

Everything else in the sentence stays the same.