Cái áo màu xanh này rất đẹp.

Cái is a classifier, not exactly an article.

In cái áo màu xanh này, cái helps introduce the noun áo in a natural Vietnamese way when talking about a specific object. A very literal breakdown is:

• cái = classifier for many everyday objects
• áo = shirt/top/garment

So cái áo này means this shirt.

It is not the same as English the or a/an. Vietnamese does not have articles in the same way English does.

Also, in everyday speech, classifiers are sometimes omitted when the meaning is already clear. So Áo này rất đẹp can also be natural, though Cái áo này rất đẹp sounds a bit more complete or specific.

Not always. Áo is a fairly broad word for an upper-body garment.

Depending on context, it can mean:

• shirt
• blouse
• top
• jacket
• coat

So if the translation says shirt, that is fine, but the Vietnamese word itself is a bit more general than the English word shirt.

If you want to be more specific, Vietnamese often adds another word, for example:

• áo sơ mi = dress shirt / button-up shirt
• áo thun = T-shirt
• áo khoác = jacket

Because màu means color, so áo màu xanh literally means a shirt of green/blue color.

Vietnamese often allows both:

• áo xanh = green/blue shirt
• áo màu xanh = shirt that is green/blue in color

The version with màu is a little more explicit. It can feel slightly more descriptive or careful.

So:

• Cái áo xanh này rất đẹp = very natural
• Cái áo màu xanh này rất đẹp = also natural, with the color stated more explicitly

It can mean either green or blue, depending on context.

This is a very common point of confusion for English speakers. Vietnamese xanh covers a wider color range than English green or blue.

If speakers want to be more specific, they often say:

• xanh lá cây = green
• xanh dương / xanh da trời = blue

So in your sentence, xanh by itself is somewhat ambiguous unless the context or translation already makes it clear.

Because Vietnamese demonstratives usually come after the noun phrase.

So:

• cái áo này = this shirt
• cái áo đó = that shirt
• cái áo kia = that shirt over there

When there are modifiers, này usually comes after them:

• cái áo màu xanh này

So the order is basically:

• classifier + noun + description + this/that

That is normal Vietnamese word order.

Vietnamese often does not use a verb meaning to be before adjectives.

So:

• Cái áo màu xanh này rất đẹp = This green shirt is very beautiful.

Here, đẹp acts as the predicate by itself, and rất modifies it.

This is different from English, where you must say is beautiful.

Also, you normally would not use là here.
Using là before an adjective like đẹp would sound unnatural in standard Vietnamese.

A useful contrast:

• Nó rất đẹp = It is very beautiful.
• Nó là bác sĩ = He/She is a doctor.

So là is common when linking something to a noun, not usually to an adjective.

Rất means very.

So:

• đẹp = beautiful
• rất đẹp = very beautiful

Yes, you can leave it out:

• Cái áo màu xanh này đẹp. = This green shirt is beautiful.

That is still grammatical and natural. Adding rất just makes the praise stronger.

A helpful breakdown is:

• Cái = classifier
• áo = noun
• màu xanh = color description
• này = this
• rất đẹp = very beautiful

So the structure is:

classifier + noun + modifier + demonstrative + predicate adjective

More visually:

• Cái áo màu xanh này = this green/blue shirt
• rất đẹp = is very beautiful

This word order can feel unusual to English speakers because English would put this before the noun and often place some modifiers differently.

Yes, absolutely.

That version is probably even more common in everyday speech:

• Cái áo xanh này rất đẹp.

It means essentially the same thing as:

• Cái áo màu xanh này rất đẹp.

The difference is small:

• áo xanh = green/blue shirt
• áo màu xanh = shirt that is green/blue in color

The second version is a bit more explicit because it includes màu.

You can often omit cái, especially in conversation.

So all of these can be natural:

• Cái áo màu xanh này rất đẹp.
• Áo màu xanh này rất đẹp.
• Cái áo xanh này rất đẹp.
• Áo xanh này rất đẹp.

Keeping cái can make the noun phrase sound slightly more concrete or complete, but omitting it is very common when the noun is already clear.

For learners, it is useful to recognize classifiers, but also important to know that native speakers do not always use them in every possible place.