Dane potwierdzają ten fakt.

Here dane means data.

In Polish, dane is normally treated as a plural noun, so the verb must also be plural:

• dane potwierdzają = the data confirm
• not dane potwierdza

There is a singular form dana, but in modern everyday Polish it is rare and usually not what learners need first. In normal usage, just remember:

• te dane = this data / these data
• dane są = the data are

Also be careful: Polish data usually means date (calendar date), not data in the English sense.

Potwierdzają is the 3rd person plural present tense of potwierdzać (to confirm).

It matches the subject dane, which is plural.

A quick comparison:

• potwierdzam = I confirm
• potwierdzasz = you confirm
• potwierdza = he/she/it confirms
• potwierdzamy = we confirm
• potwierdzacie = you (plural) confirm
• potwierdzają = they confirm

So:

• Dane potwierdzają... = The data confirm...

Ten fakt is the direct object, so it is in the accusative case.

However, fakt is a masculine inanimate noun, and for many masculine inanimate nouns, the accusative singular looks exactly like the nominative singular.

So:

• nominative: ten fakt
• accusative: ten fakt

That is why it does not visibly change.

If it were a masculine animate noun, you would often see a different form in the accusative.

Because after a normal affirmative transitive verb like potwierdzać, the direct object usually goes in the accusative, not the genitive.

So:

• potwierdzać co? → ten fakt

Faktu is a different case form, usually genitive singular, and it would be used in other structures, not here.

For example:

• nie ma tego faktu would still sound odd in many contexts, but faktu is the kind of form you see in genitive environments
• in this sentence, the correct object is ten fakt

Dane is in the nominative plural, because it is the subject of the sentence.

You can test it by asking:

• Co potwierdza ten fakt? → actually, because the subject is plural, better:
• Co potwierdza / potwierdzają ten fakt? → dane

So the structure is:

• dane = subject, nominative plural
• potwierdzają = verb, 3rd person plural
• ten fakt = object, accusative singular

No, Polish word order is relatively flexible.

The neutral order here is:

• Dane potwierdzają ten fakt.

But you could also say:

• Ten fakt potwierdzają dane.

Both are grammatically correct. The difference is mainly emphasis:

• Dane potwierdzają ten fakt. → neutral, straightforward
• Ten fakt potwierdzają dane. → puts more focus on this fact

Because Polish uses case endings, word order can move around more than in English.

Polish has no articles, so there is no direct equivalent of English a/an/the.

That means:

• Dane potwierdzają ten fakt.

does not need any article before dane or fakt.

Polish expresses definiteness in other ways, for example through:

• context
• word order
• demonstratives such as ten = this / that

Here ten fakt makes the noun more specific: this fact.

Ten is a demonstrative adjective, usually meaning this.

So:

• ten fakt = this fact

It agrees with fakt in gender, number, and case.

Because fakt is:

• masculine
• singular
• accusative here, but masculine inanimate accusative looks like nominative

the correct form is ten.

Some related forms are:

• ta książka = this book
• to pytanie = this question
• te dane = these data

Potwierdzać is imperfective.

Its perfective partner is usually potwierdzić.

That matters because in Polish:

• imperfective verbs can have a true present tense
• perfective verbs do not have a true present meaning; their present-looking forms usually refer to the future

So:

• Dane potwierdzają ten fakt. = The data confirm / are confirming this fact.
• Dane potwierdzą ten fakt. = The data will confirm this fact.

In your sentence, the imperfective potwierdzają is natural for a general statement or present-time statement.

Yes, depending on context.

Polish present tense often covers both:

• simple present
• present progressive

So potwierdzają can mean:

• confirm
• are confirming

In many contexts, the more natural English translation is:

• The data confirm this fact.

because it sounds like a general or objective statement.

A rough pronunciation guide is:

pot-vyer-DZA-yon

A bit more carefully:

• po = like po in pot, but shorter
• twier = roughly tvyer
• dza = like jah with a voiced dz sound before it
• ją = roughly nasal yon

The stress is on the second-to-last syllable:

• potwierDZAją

That second-to-last stress rule works for most Polish words.

It could be.

Both are possible:

• Dane potwierdzają ten fakt.
• Te dane potwierdzają ten fakt.

The version without te is more general: Data confirm this fact.

The version with te is more specific: These data confirm this fact.

So the original sentence is fine; it is just slightly less explicitly pointed.

Yes, fakt is a masculine noun.

That is why it combines with:

• ten fakt

not:

• ta fakt
• to fakt

This matters for agreement with adjectives, demonstratives, and sometimes past-tense verbs.

For example:

• ważny fakt = an important fact
• ten ważny fakt = this important fact

In standard Polish, dane normally takes a plural verb.

So the normal pattern is:

• Dane wskazują...
• Dane potwierdzają...
• Dane pokazują...

Using a singular verb with dane would sound wrong to most speakers in normal modern Polish.

So for learners, the safest rule is simple:

• dane = plural grammar

A few common alternatives are:

• Dane wskazują na ten fakt. = The data point to this fact.
• Dane dowodzą tego. = The data prove this.
• Dane to potwierdzają. = The data confirm it / confirm that.
• Dane świadczą o tym. = The data indicate this / are evidence of this.

These are not always identical in tone, but they are all common in formal or analytical Polish.