Na wystawie widzieliśmy jedenaście obrazów.

Because Polish normally uses na with many events and public activities, including exhibitions.

So na wystawie means at the exhibition.

This is idiomatic Polish:

• na wystawie = at the exhibition
• na koncercie = at the concert
• na spotkaniu = at the meeting

Even though na often literally means on, here it simply means at in natural English.

Wystawie is the locative singular form of wystawa.

The pattern is:

• dictionary form: wystawa
• after na in this meaning: na wystawie

So the preposition na here requires the locative.

Because Polish often leaves out subject pronouns when the verb already shows who is doing the action.

In widzieliśmy, the ending -śmy already tells you the subject is we.

So:

• widzieliśmy = we saw
• my widzieliśmy = we saw, but with extra emphasis on we

In most normal sentences, the pronoun my is unnecessary.

Widzieliśmy is the past tense, 1st person plural form of widzieć = to see.

So it means we saw.

It also shows a gender distinction that English does not have:

• widzieliśmy is used by a mixed group or an all-male group
• widziałyśmy is used by an all-female group

That distinction appears in the past tense in Polish.

This is about aspect, which is very important in Polish.

• widzieć is imperfective
• zobaczyć is perfective

In a sentence like this, widzieliśmy is a very natural, neutral way to say we saw.

Zobaczyliśmy would sound more like:

• we caught sight of
• we managed to see
• we saw them at that moment

So both can be possible in some contexts, but widzieliśmy is the more straightforward choice here.

In this sentence, the normal translation is we saw.

Even though imperfective verbs can sometimes correspond to English forms like was/were doing, that is not the most natural reading here. With widzieć in a simple past statement, we saw is usually best.

So here:

• Na wystawie widzieliśmy jedenaście obrazów. = At the exhibition, we saw eleven paintings.

Because after numerals 5 and higher, Polish normally uses the noun in the genitive plural.

Compare:

• jeden obraz = one painting
• dwa obrazy = two paintings
• trzy obrazy = three paintings
• cztery obrazy = four paintings
• pięć obrazów = five paintings
• jedenaście obrazów = eleven paintings

So obrazów is exactly what you expect after jedenaście.

Yes.

The whole expression jedenaście obrazów functions as the direct object of widzieliśmy, but inside that expression the numeral jedenaście requires the noun to be in the genitive plural.

So:

• whole phrase: direct object
• noun inside the phrase: genitive plural

This is a very common Polish pattern with numbers 5+.

It is functioning as the object of the verb, so it is in the accusative. But for jedenaście, the nominative and accusative forms look the same.

So you still see jedenaście.

In other cases, it does change. For example:

• z jedenastoma obrazami = with eleven paintings

So the numeral does decline, just not visibly in this sentence.

The dictionary forms are:

• wystawa = exhibition
• obraz = painting / picture

In the sentence, they appear as:

• wystawie = locative singular of wystawa
• obrazów = genitive plural of obraz

So when looking words up, you would search for wystawa and obraz.

Yes, the word order could be different.

Polish word order is more flexible than English because endings show grammatical relationships. Starting with Na wystawie puts the setting first, something like:

At the exhibition, we saw eleven paintings.

You could also say:

• Widzieliśmy jedenaście obrazów na wystawie.

That is still correct, but the emphasis is slightly different. The original version sounds very natural because it introduces the place first.

Because Polish has no articles.

English distinguishes:

• a painting
• the painting

Polish does not do that with separate words. It relies on context instead.

So jedenaście obrazów can mean simply eleven paintings, and the context tells you whether they are specific or not.