Ons vier die sukses.

Here, ons means we.

Afrikaans ons can also mean us or our in other contexts, but in this sentence it is the subject of the verb, so the natural meaning is we.

Here, vier is the verb to celebrate.

So Ons vier die sukses means We celebrate the success or We are celebrating the success, depending on context.

A common point of confusion: vier can also mean four in Afrikaans. The context tells you which meaning is intended.

• Ons vier die sukses = We celebrate the success
• vier boeke = four books

Because Afrikaans verbs usually do not change form the way English verbs do.

In the present tense, you normally use the same verb form with different subjects:

• ek vier = I celebrate
• jy vier = you celebrate
• ons vier = we celebrate
• hulle vier = they celebrate

So vier stays vier.

Die is the definite article, meaning the.

So:

• die sukses = the success

Afrikaans uses die for the in both singular and plural nouns, so it is a very common and useful word.

No. In Afrikaans, die is usually pronounced roughly like dee.

So in this sentence:

• die sukses sounds roughly like dee suk-SESS

That pronunciation is very important, because an English speaker might otherwise read it the wrong way.

Yes, in this basic sentence the word order is very similar to English:

• Ons = subject
• vier = verb
• die sukses = object

So it follows a normal subject–verb–object pattern:

• Ons vier die sukses.
• We celebrate the success.

This makes the sentence quite straightforward for English speakers.

Sukses means success.

It is a close cognate with the English word, so it is easy to recognize. In this sentence, with die, it refers to a specific success or achievement:

• die sukses = the success

Depending on context, that could mean a victory, a good result, or a successful outcome.

You can, but it changes the feel of the sentence.

• Ons vier die sukses = We celebrate the success
  This points to a specific success.

• Ons vier sukses = more like We celebrate success in a general or abstract sense

If you are talking about one particular achievement, die is the natural choice.

A rough English-friendly pronunciation is:

ons feer dee suk-SESS

A few notes:

• Ons: roughly ons
• vier: roughly feer
• die: dee
• sukses: roughly suk-SESS

The stress is usually strongest on the second syllable of sukses.

It can mean several things, depending on the sentence:

• ons = we
• ons = us
• ons = our

For example:

• Ons vier die sukses. = We celebrate the success.
• Hulle sien ons. = They see us.
• Ons huis is groot. = Our house is big.

So context and sentence structure tell you which meaning is intended.