Dziś nigdzie nie wychodzę, bo z nikim się nie umówiłam.

Because Polish normally uses multiple negation. If the sentence is negative, words like nigdzie (nowhere) usually appear together with nie on the verb.

So:

• nigdzie nie wychodzę = I’m not going anywhere / I’m going nowhere

This is completely normal in Polish. Unlike standard English, it is not considered incorrect or redundant.

A few similar examples:

• Nigdy nie piję kawy. = I never drink coffee.
• Nikogo nie znam. = I don’t know anyone.
• Nic nie rozumiem. = I don’t understand anything.

Nigdzie means nowhere / to no place.

Nigdy means never.

So in this sentence:

• Dziś nigdzie nie wychodzę = Today I’m not going anywhere

Not:

• Dziś nigdy nie wychodzę — which would not make sense here

This is a very common mix-up for learners, because the words look similar.

Polish often uses the present tense to talk about a planned or intended near future, especially with verbs of movement or everyday actions.

So:

• Dziś nigdzie nie wychodzę literally looks like Today I’m not going out
• In natural English, that may mean I’m not going anywhere today

This is similar to English I’m not going out today, which is also present in form but future in meaning.

Also, wychodzić is the imperfective verb, which fits well when talking about the general action of going out, not one single completed exit.

Because the verb phrase is umówić się z kimś = to arrange to meet with someone / to make plans with someone.

The preposition z here means with, and after z you need the instrumental case.

So:

• kto = who
• kim = whom / with whom
• z kimś = with someone
• z nikim = with no one / with nobody

That is why the sentence says:

• bo z nikim się nie umówiłam = because I didn’t make plans with anyone

Because the verb is umówić się (perfective) or umawiać się (imperfective), not just umówić in this meaning.

Umówić się z kimś means:

• to arrange to meet someone
• to make plans with someone
• to agree on a meeting

The się is part of the verb phrase.

Compare:

• Umówiłam się z Anią. = I arranged to meet Ania / I made plans with Ania.
• Nie umówiłam się z nikim. = I didn’t make plans with anyone.

Umówiłam is the past tense, feminine singular form.

So this sentence is spoken by a woman.

• umówiłam = I did arrange / I arranged (female speaker)
• umówiłem = same meaning, but said by a man

So:

• bo z nikim się nie umówiłam = if the speaker is female
• bo z nikim się nie umówiłem = if the speaker is male

This is one of the important differences between Polish and English: past tense often shows the speaker’s gender.

Because it refers to something completed before now: the speaker did not make any arrangement earlier, and that is the reason they are not going out today.

The logic is:

• Today I’m not going anywhere
• because I didn’t arrange to meet anyone

So the first part describes the current plan for today, while the second part explains the earlier reason behind it.

Using the past tense here is very natural.

Yes, both are possible, but they have slightly different styles.

• bo = because in everyday, natural speech
• ponieważ = because / since, but a bit more formal or written

So:

• Dziś nigdzie nie wychodzę, bo z nikim się nie umówiłam.
  Very natural in conversation.

You could also say:

• Dziś nigdzie nie wychodzę, ponieważ z nikim się nie umówiłam.

That is correct, just a little more formal.

Yes. Polish word order is more flexible than English, although some versions sound more natural than others.

The original:

• Dziś nigdzie nie wychodzę, bo z nikim się nie umówiłam.

is very natural.

You could also hear:

• Nigdzie dziś nie wychodzę, bo z nikim się nie umówiłam.
• Bo z nikim się nie umówiłam, dziś nigdzie nie wychodzę.

The meaning stays basically the same, but the emphasis changes:

• Dziś first emphasizes today
• Nigdzie first emphasizes nowhere
• starting with bo... sounds more marked or explanatory

For learners, the original order is a good model.

Yes. Dziś and dzisiaj both mean today.

• dziś is a bit shorter and often feels slightly more conversational or compact
• dzisiaj is also very common and completely natural

So both are fine:

• Dziś nigdzie nie wychodzę...
• Dzisiaj nigdzie nie wychodzę...

There is no important difference in meaning here.

This is a question of aspect.

• umówić się = perfective
  focuses on completing the arrangement
• umawiać się = imperfective
  focuses on the process, repetition, or general habit

In this sentence, umówiłam się is perfective because the speaker means a completed result:

• I did not make any arrangement

Compare:

• Nie umówiłam się z nikim na dziś. = I didn’t arrange to meet anyone today.
• Nie umawiam się z ludźmi przez telefon. = I don’t make arrangements with people by phone. / I don’t usually arrange meetings by phone.

So the perfective verb is the right choice here.