Learn Hardcore German: Dein Wortschatz ist schon groß, aber du willst trotzdem neue Redewendungen lernen. - Your vocabulary is already large, but you still want to learn new idioms.

The subject of the sentence is Dein Wortschatz (“your vocabulary”), which is 3rd person singular, not “you”.
So we need the 3rd person singular of sein → ist.

Compare:

Du bist müde. – You are tired. (subject: du → 2nd person singular)
Dein Hund ist müde. – Your dog is tired. (subject: dein Hund → 3rd person singular)
Dein Wortschatz ist groß. – Your vocabulary is big. (subject: dein Wortschatz → 3rd person singular)

What exactly does schon mean here in ist schon groß?

Here, schon means “already”, and it adds a slightly positive, reassuring tone:

Dein Wortschatz ist schon groß
= Your vocabulary is already large (i.e. you’ve learned a lot so far).

Other common uses of schon:

Literal “already” in time:
- Bist du schon fertig? – Are you finished already?
Softening / reassuring particle (more advanced use):
- Das wird schon klappen. – It’ll be fine / It’ll work out.

In your sentence, it’s mainly the straightforward “already” with a hint of praise.

Why use groß to describe vocabulary? Could you also say something else?

In German, groß can be used for size in a more abstract sense, similar to English “big” or “large”.

ein großer Wortschatz = a large vocabulary

Other very natural options:

umfangreich – extensive
Dein Wortschatz ist schon umfangreich.
sehr groß – very large
Dein Wortschatz ist schon sehr groß.

Groß is the most straightforward everyday choice; umfangreich sounds a bit more formal or “textbook-like”.

What does aber do here, and why is there a comma before it?

Aber is a coordinating conjunction meaning “but”. It connects two main clauses that contrast with each other:

Clause 1: Dein Wortschatz ist schon groß
Clause 2: du willst trotzdem neue Redewendungen lernen

German grammar requires a comma before coordinating conjunctions like: und, oder, aber, sondern, denn when they link two clauses.

So the structure is:

[Main clause], aber [main clause].

Just like in English: “..., but ...”

Why is it du willst ... lernen and not something like du lernst?

The verb wollen expresses volition / intention – what you want to do, not what you are doing right now.

du lernst – you are learning / you learn
du willst lernen – you want to learn

In your sentence, the idea is:

Your vocabulary is large already,
but you still want to learn new idioms.

So willst lernen (want to learn) is more accurate than simply lernst (are learning).

What’s the difference between willst and möchtest here?

Both can express a wish, but there’s a difference in tone:

du willst lernen – you want to learn
More direct, stronger desire, can sound more determined or blunt.
du möchtest lernen – you would like to learn
Softer, more polite, often used in polite requests.

In your sentence, both are grammatically fine:

... aber du willst trotzdem neue Redewendungen lernen.
... aber du möchtest trotzdem neue Redewendungen lernen.

The first sounds a bit more determined; the second a bit more gentle.

How does the word order work in du willst trotzdem neue Redewendungen lernen?

The structure is:

du – subject
willst – conjugated (finite) verb in 2nd position
trotzdem – adverb
neue Redewendungen – object (accusative)
lernen – infinitive at the end

With a modal verb like wollen, German puts:

the finite modal verb (willst) in 2nd position
the main verb infinitive (lernen) at the very end

So:

du willst ... lernen
du musst ... lernen
du kannst ... lernen

The adverb trotzdem and the object neue Redewendungen go in the “middle field” between willst and lernen.

What does trotzdem mean, and where can it go in the sentence?

Trotzdem means roughly “nevertheless / still / anyway”. It expresses that something happens despite what was just said.

In your sentence:

Your vocabulary is already large,
but nevertheless you want to learn new idioms.

Possible positions:

As in the original:
- Du willst trotzdem neue Redewendungen lernen.
At the beginning of the clause, which is also very natural:
- Trotzdem willst du neue Redewendungen lernen.

What you normally don’t say (sounds awkward):

Du willst neue Redewendungen trotzdem lernen.
(This word order is possible, but it suggests a special emphasis on “in spite of everything else, you will still learn them”, and usually natives would place trotzdem earlier.)

The most neutral choices are either sentence-internal after the verb (willst trotzdem ...) or at the beginning (Trotzdem willst du ...).

What exactly are Redewendungen? Is that the same as “expressions” or “idioms”?

Redewendungen (singular: die Redewendung) are fixed or semi-fixed phrases whose meaning is often not completely literal.

They’re close to what English calls idioms or set expressions, for example:

ins kalte Wasser springen – to jump in at the deep end
um den heißen Brei herumreden – to beat around the bush

Related terms:

Ausdruck (pl. Ausdrücke) – expression (more general)
Phrase (pl. Phrasen) – phrase (often used in linguistics)
Sprichwort (pl. Sprichwörter) – proverb (a fixed saying with a moral or wisdom)

So Redewendungen are especially those idiomatic word combinations you can’t just translate word-for-word.

Why is it neue Redewendungen and not neuen Redewendungen?

This is about adjective endings.

Redewendungen is plural: die Redewendungen
In the sentence, neue Redewendungen is a direct object → accusative plural

For accusative plural with an indefinite context (no article in front), the adjective ending is -e:

neue Redewendungen
alte Bücher
gute Freunde

You would get -en in other patterns, for example with a definite article in plural:

die neuen Redewendungen (nom./acc. plural with die)

Since there’s no article here, neue Redewendungen is correct.

Which cases appear in the sentence, and how can I recognise them?

Two noun phrases are important:

Dein Wortschatz
- Role: subject of ist
- Case: nominative
- Test: Who/what is big? → Dein Wortschatz.
neue Redewendungen
- Role: direct object of willst ... lernen
- Case: accusative
- Test: What do you want to learn? → neue Redewendungen.

There are no dative or genitive forms in this sentence.

Could I say Dein Wortschatz ist schon groß, aber trotzdem willst du neue Redewendungen lernen? Is that different?

Yes, that version is perfectly correct:

Dein Wortschatz ist schon groß, aber trotzdem willst du neue Redewendungen lernen.

Here, trotzdem comes right after aber and before the verb willst, so the clause is:

trotzdem (initial element)
willst (finite verb in 2nd position)
du (subject)
neue Redewendungen lernen (rest)

Meaning and tone are essentially the same as:

..., aber du willst trotzdem neue Redewendungen lernen.

Putting trotzdem earlier slightly highlights the “nevertheless” more, but both are natural.

Does willst lernen express future, or should I use wirst lernen for “you will learn”?

In German, it’s very common to use the present tense to talk about the near future or general plans, especially with verbs like wollen:

Du willst neue Redewendungen lernen.
= You intend / want to learn new idioms (in the future).

Werden + infinitive (du wirst lernen) is the “will-future”, but it’s used less often than English will, and it usually:

emphasizes prediction, or
is used when the future time needs to be very clear from context.

Here, willst lernen (want to learn) is the natural way to express your intention to do this in the (near) future.