Jeśli będzie gorąco, założę sandały zamiast butów, chyba że zacznie padać.

Because gorąco here is an adverb-like predicate meaning it will be hot in the sense of the weather/temperature will be hot.

In Polish, weather expressions often use:

• jest zimno = it is cold
• jest ciepło = it is warm
• jest gorąco = it is hot

So:

• będzie gorąco = it will be hot

By contrast, gorący / gorąca / gorące is an adjective and must describe a noun:

• gorąca kawa = hot coffee
• gorący dzień = a hot day

So in this sentence, będzie gorąco is the natural weather expression.

Yes. Będzie is the future form of być (to be), so jeśli będzie gorąco literally means if it will be hot, although in natural English we say if it is hot.

This is an important difference between English and Polish:

• English usually uses present tense after if for future meaning:
  If it’s hot, I’ll wear sandals.
• Polish normally uses future tense if the meaning is future:
  Jeśli będzie gorąco, założę sandały.

So this is completely normal Polish grammar.

Założę is the 1st person singular future form of założyć, which here means to put on / to put onto oneself.

So:

• założę sandały = I will put on sandals

In Polish, verbs often distinguish between:

• put on an item
• be wearing an item

For example:

• Założę sandały = I’ll put on sandals
• Będę mieć na sobie sandały or simply contextually będę w sandałach = I’ll be wearing sandals / I’ll be in sandals

Polish often prefers założyć when talking about choosing what to wear.

Because the sentence refers to a single completed action in the future: I’ll put on sandals.

In Polish:

• założyć is perfective
• its future is a simple form: założę

Perfective verbs are commonly used for one-time completed future actions.

An imperfective counterpart would be zakładać, but that is not normally used here for a simple future choice of clothing. Będę zakładać sandały would sound more like repeated or ongoing action, not the natural meaning here.

So założę is the right choice.

Because the two nouns are controlled by different parts of the sentence.

1. założę sandały

The verb założyć takes a direct object in the accusative case.

• nominative: sandały
• accusative: sandały

For plural inanimate nouns, nominative and accusative are often the same, so sandały stays sandały.

2. zamiast butów

The preposition zamiast requires the genitive case.

• buty = shoes
• genitive plural: butów

So:

• sandały = accusative, because they are what I will put on
• butów = genitive, because it follows zamiast

Yes, zamiast normally takes the genitive case and means instead of.

Examples:

• zamiast kawy = instead of coffee
• zamiast herbaty = instead of tea
• zamiast butów = instead of shoes

So in your sentence:

• założę sandały zamiast butów = I’ll put on sandals instead of shoes

This is a very useful structure to remember:

• zamiast + genitive

Yes, in this sentence chyba że means unless.

So:

• chyba że zacznie padać = unless it starts raining

Literally, chyba że is something like except if / unless. It introduces an exception to what was just said.

Examples:

• Przyjdę, chyba że będę chory. = I’ll come, unless I’m sick.
• Pójdziemy na spacer, chyba że będzie padać. = We’ll go for a walk, unless it’s raining.

It is a very common and natural expression in Polish.

Zacznie padać means it will start raining, so it focuses on the beginning of the rain.

Breakdown:

• zacznie = will begin / will start
• padać = to fall; in weather context, to rain / to snow depending on context

So:

• zacznie padać = it starts to rain / it begins raining

Other options would mean slightly different things:

• będzie padać = it will be raining / it will rain continuously
• spadnie deszcz is not the usual natural way to say it will rain

The sentence uses zacznie padać because it means: I’ll wear sandals, unless the weather changes and rain begins.

Yes, literally padać means to fall, but it is also the standard verb used for precipitation.

Examples:

• Pada deszcz. = It’s raining.
• Pada śnieg. = It’s snowing.
• Zaczyna padać. = It’s starting to rain / snow.

In this sentence, because there is no noun like deszcz or śnieg, the default interpretation is usually rain:

• zacznie padać = it will start raining

So this is a very common weather verb in Polish.

Yes. Polish word order is more flexible than English, although the original sentence is very natural.

Original:

• Jeśli będzie gorąco, założę sandały zamiast butów, chyba że zacznie padać.

Possible variations:

• Założę sandały zamiast butów, jeśli będzie gorąco, chyba że zacznie padać.
• Chyba że zacznie padać, jeśli będzie gorąco, założę sandały zamiast butów.
  This one is grammatically possible but much less natural stylistically.

Why use the original order?

• It presents the condition first: if it’s hot
• then the action: I’ll put on sandals
• then the exception: unless it starts raining

That order is clear and natural.

Because Polish punctuation usually separates subordinate clauses with commas.

Here you have:

1. Jeśli będzie gorąco — an if clause
2. założę sandały zamiast butów — the main clause
3. chyba że zacznie padać — an exception clause (unless)

So the commas mark the boundaries between these parts:

• Jeśli będzie gorąco, założę sandały zamiast butów, chyba że zacznie padać.

This is standard Polish punctuation.

Yes, in natural English translation butów is often rendered as shoes, even though sandals are technically footwear too.

In Polish:

• buty is a broad everyday word for shoes/footwear
• sandały is a more specific type

So sandały zamiast butów sounds like:

• sandals instead of regular closed shoes

That is completely natural in Polish.

Sometimes, but jeśli is the clearest standard choice for if.

• jeśli = if
• gdy can mean when and sometimes if, depending on context
• jak can mean when in some colloquial contexts, but not as a direct replacement in every situation

In this sentence, jeśli is best because it clearly introduces a condition:

• Jeśli będzie gorąco... = If it’s hot...

So for learners, jeśli is the safest and most direct option.

Yes, it sounds natural and idiomatic.

A Polish speaker would easily say something like:

• Jeśli będzie gorąco, założę sandały zamiast butów, chyba że zacznie padać.

It combines several very common patterns:

• jeśli + future
• weather expression będzie gorąco
• clothing verb założę
• zamiast + genitive
• chyba że
• weather verb zacznie padać

So it is a very useful model sentence for real-life Polish.