Remélem, hogy a csere gyors lesz.

It comes from the verb remél, meaning to hope.

• remélek = I hope in the indefinite conjugation
• remélem = I hope it / I hope that... in the definite conjugation

In Remélem, hogy..., Hungarian normally uses the definite form because the whole hogy-clause functions like a definite object: I hope that...

So Remélem, hogy a csere gyors lesz. is the standard way to say I hope that the exchange/replacement will be quick.

Hungarian usually leaves out subject pronouns when the verb ending already shows the person.

In Remélem, the ending tells you the subject is I. So én is not necessary.

• Remélem... = I hope...
• Én remélem... = I hope... with extra emphasis on I

So the version without én is the normal neutral one.

Hogy means that and introduces a subordinate clause.

So:

• Remélem = I hope
• hogy a csere gyors lesz = that the exchange/replacement will be quick

Very literally, the structure is:

I hope + that + the replacement will be quick.

Yes, very often.

You can say:

• Remélem, hogy a csere gyors lesz.
• Remélem, a csere gyors lesz.

Both are natural. The version with hogy is a bit more explicit; the version without it can sound slightly more streamlined or conversational.

Because Hungarian normally separates the main clause from the subordinate clause with a comma.

So:

• Remélem, hogy...

The comma is standard punctuation here. Even if hogy is omitted, you will still often see the pause marked with a comma:

• Remélem, a csere gyors lesz.

No. This is a very common beginner confusion.

Hungarian a / az means the, not English a/an.

So:

• a csere = the exchange / the replacement

The Hungarian indefinite article is egy:

• egy csere = an exchange / a replacement

Hungarian has two forms of the definite article:

• a before a consonant sound
• az before a vowel sound

Since csere begins with cs, which is a consonant sound, the correct form is:

• a csere

Compare:

• a csere
• az autó

Csere can mean exchange, swap, or replacement, depending on context.

So this sentence could refer to things like:

• a product replacement
• a part being replaced
• an exchange process
• a swap of one item for another

The exact English word depends on the situation, but grammatically csere is the subject of the clause here.

Lesz is the future form of lenni (to be) in the third person singular.

So:

• gyors lesz = will be quick

Hungarian does not need a separate word like English will here. The future meaning is already built into lesz.

A useful comparison:

• A csere gyors. = The exchange/replacement is quick.
• A csere gyors lesz. = The exchange/replacement will be quick.

In a neutral sentence like this, Hungarian normally puts the adjective before lesz:

• a csere gyors lesz

This is the ordinary, unmarked word order for will be quick.

If you changed the order to lesz gyors, it would sound marked, unusual, or strongly emphasis-driven in most contexts. So learners should treat gyors lesz as the normal pattern.

Because after to be, Hungarian uses an adjective, not an adverb.

• gyors = quick
• gyorsan = quickly

Here the sentence means the replacement will be quick, so you need the adjective:

• A csere gyors lesz.

If you used gyorsan, that would describe how an action is done, not what something is.