Công viên rất đông vui cuối tuần này.

Vietnamese often does not use a verb like to be when describing something with an adjective.

So:

• Công viên = park
• rất đông vui = very crowded/lively
• cuối tuần này = this weekend

The structure is basically:

noun + degree word + adjective + time expression

So Công viên rất đông vui cuối tuần này naturally means The park is very crowded and lively this weekend without needing a separate word for is.

It is made from two words:

• đông = crowded
• vui = happy, fun, lively

Together, đông vui is a very common combination meaning something like:

• crowded and lively
• busy and cheerful
• full of people and fun

So it is really two ideas working together, but learners should treat it as a very natural set phrase.

Rất means very. It intensifies the description:

• Công viên đông vui = The park is crowded/lively.
• Công viên rất đông vui = The park is very crowded/lively.

It is optional, but it makes the sentence stronger.

In Vietnamese, time expressions often come either at the beginning or the end of a sentence.

So these are both natural:

• Công viên rất đông vui cuối tuần này.
• Cuối tuần này, công viên rất đông vui.

Putting cuối tuần này at the end sounds very natural and keeps the main description first: The park is very lively, then this weekend.

Yes. Này means this.

In cuối tuần này, it modifies the whole time phrase cuối tuần:

• cuối tuần = weekend
• cuối tuần này = this weekend

So này comes after the noun phrase in Vietnamese. This is very common:

• công viên này = this park
• tuần này = this week
• cuối tuần này = this weekend

Unlike English, Vietnamese usually puts this-type words after the noun.

Vietnamese often allows time expressions without a preposition.

So cuối tuần này by itself already means this weekend. You do not need vào.

You could say:

• Công viên rất đông vui cuối tuần này.

And that is perfectly natural.

Sometimes vào can be used before time expressions, but in simple sentences like this, it is often omitted.

By itself, công viên is just park as a noun. Vietnamese does not mark articles like English a or the.

So depending on context, it could mean:

• the park
• a park
• parks in a general statement

But in this sentence, most learners will understand it as the park or the park we are talking about. Context decides that, not the noun form itself.

Yes. That would mean This park is very crowded and lively this weekend.

Compare:

• Công viên rất đông vui cuối tuần này. = The park / parks are very lively this weekend.
• Công viên này rất đông vui cuối tuần này. = This park is very lively this weekend.

Adding này after công viên makes the park itself specifically this park.

Đông focuses on the number of people:

• đông = crowded

Đông vui adds a positive social feeling:

• đông vui = crowded in a lively, pleasant, cheerful way

So if you say:

• Công viên đông = The park is crowded.
• Công viên đông vui = The park is crowded and lively.

The second one sounds warmer and more positive.

It means this weekend, specifically, because of này.

• cuối tuần = weekend / on weekends, depending on context
• cuối tuần này = this weekend

If you wanted a more general meaning like The park is lively on weekends, you would more likely say:

• Công viên rất đông vui vào cuối tuần.
• or Công viên rất đông vui cuối tuần.

So này makes it specific.

Yes. This sentence follows a very common Vietnamese pattern:

subject + degree word + descriptive word(s) + time expression

So:

• Công viên = subject
• rất = degree word
• đông vui = description
• cuối tuần này = time expression

This is a very normal and useful pattern to learn for everyday Vietnamese.