Trung tâm cứu hộ động vật hoang dã sạch.

A natural breakdown is:

• trung tâm = center
• cứu hộ = rescue, give aid, save/protect
• động vật hoang dã = wild animals, wildlife
• sạch = clean

So trung tâm cứu hộ động vật hoang dã means wildlife rescue center, and sạch adds the idea clean.

In Vietnamese, adjectives usually come after the noun they describe.

So where English says:

• a clean center

Vietnamese says:

• trung tâm sạch

In your sentence, sạch comes after the whole noun phrase trung tâm cứu hộ động vật hoang dã.

If the intended meaning is The wildlife rescue center is clean, Vietnamese often expresses that simply as:

• [noun phrase] + adjective

So sạch appears at the end.

Because Vietnamese often does not use a copula like English is before adjectives.

English:

• The center is clean.

Vietnamese:

• Trung tâm ... sạch.

This is completely normal.

A very common learner mistake is trying to insert là here:

• Trung tâm ... là sạch ✘

That is usually not correct. Là is mainly used when linking one noun to another, not before ordinary descriptive adjectives.

It describes động vật.

So:

• động vật hoang dã = wild animals / wildlife

The structure is:

• trung tâm = center
• cứu hộ động vật hoang dã = rescuing wild animals

So this is a center for rescuing wild animals, not a wild center.

The head noun comes first in Vietnamese, and the words after it narrow down what kind of thing it is.

So:

• trung tâm = center
• trung tâm cứu hộ = rescue center
• trung tâm cứu hộ động vật hoang dã = wildlife rescue center

You can think of it almost like:

• center [for] rescuing wild animals

Vietnamese often stacks information this way instead of using many prepositions like English does.

It is originally a verb / verbal expression meaning to rescue or to provide aid/protection, but in Vietnamese, verbs can also directly modify nouns.

So in:

• trung tâm cứu hộ động vật hoang dã

cứu hộ động vật hoang dã acts like a modifier of trung tâm.

In English, we might use:

• a rescue center
• a center that rescues wildlife
• a center for rescuing wildlife

Vietnamese can express this more compactly.

Sạch is perfectly fine.

• sạch = clean
• sạch sẽ = clean, neat, nice and clean

Sạch sẽ can sound a little more descriptive or polished, but sạch is very common and natural.

So both can work:

• Trung tâm cứu hộ động vật hoang dã sạch.
• Trung tâm cứu hộ động vật hoang dã sạch sẽ.

The second may feel slightly fuller, but the first is not wrong.

Vietnamese does not have articles like English a/an/the.

So trung tâm can mean:

• a center
• the center
• centers in a general sense

The exact meaning depends on context.

If you want to make it more specific, Vietnamese can add words such as:

• một = a, one
• này = this
• đó/kia = that

For example:

• Một trung tâm cứu hộ động vật hoang dã sạch = a clean wildlife rescue center
• Trung tâm cứu hộ động vật hoang dã này sạch = this wildlife rescue center is clean

It can depend on context.

As written, Trung tâm cứu hộ động vật hoang dã sạch could be understood as:

• The wildlife rescue center is clean
  or
• a clean wildlife rescue center

Vietnamese often leaves this kind of distinction to context, punctuation, and intonation.

If you want to make it more clearly a sentence, you could add something like:

• Trung tâm cứu hộ động vật hoang dã này sạch. = This wildlife rescue center is clean.

If you want to make it more clearly just a noun phrase, context usually does that for you.

You can add rất before the adjective:

• Trung tâm cứu hộ động vật hoang dã rất sạch.

Here:

• rất = very
• rất sạch = very clean

This is one of the most common ways to intensify an adjective in Vietnamese.