Wir besprechen, warum der Schwierigkeitsgrad so hoch ist.

Because warum der Schwierigkeitsgrad so hoch ist is a subordinate clause. In German, subordinate clauses are normally separated from the main clause with a comma.

• Main clause: Wir besprechen
• Subordinate clause: warum der Schwierigkeitsgrad so hoch ist

So the comma is required, not optional.

Because warum introduces a subordinate clause, and in German subordinate clauses the conjugated verb usually goes to the end.

Compare:

• Main clause word order: Der Schwierigkeitsgrad ist so hoch.
• Subordinate clause word order: ..., warum der Schwierigkeitsgrad so hoch ist.

This verb-final pattern is one of the most important features of German subordinate clauses.

Here, der Schwierigkeitsgrad is the subject of the subordinate clause, so it must be in the nominative case.

Inside the clause warum der Schwierigkeitsgrad so hoch ist:

• der Schwierigkeitsgrad = subject
• ist = verb
• so hoch = predicate adjective

If it were a direct object, you might see den, but here it is the thing that is high, so nominative der is correct.

Besprechen is a verb that usually takes a direct object. It often means to discuss, to go over, or to talk through something.

Examples:

• Wir besprechen das Problem.
• Wir besprechen den Plan.

In your sentence, the thing being discussed is not a simple noun phrase, but a whole clause:

• Wir besprechen, warum ...

So German does not need a preposition like English often does in expressions such as talk about. German simply uses besprechen + object/clause.

It is functioning like an introducer of an indirect question.

This is not a direct question like:

• Warum ist der Schwierigkeitsgrad so hoch?

Instead, it is an embedded or indirect question inside a larger sentence:

• Wir besprechen, warum der Schwierigkeitsgrad so hoch ist.

So warum still means why, but the whole clause becomes subordinate, which is why the verb moves to the end.

So here means so in the sense of to such a degree.

• hoch = high
• so hoch = so high / that high

It emphasizes the degree. Without so, the sentence would still be grammatical:

• ..., warum der Schwierigkeitsgrad hoch ist.

But so hoch sounds more natural if you want to stress that the difficulty level is notably high.

Because hoch is a predicate adjective here, not an adjective directly in front of a noun.

Compare:

• der hohe Schwierigkeitsgrad → adjective before a noun, so it takes an ending
• der Schwierigkeitsgrad ist hoch → predicate adjective after sein, so no ending

In your sentence, hoch belongs to ist:

• der Schwierigkeitsgrad ... ist hoch

That is why it stays in the basic form hoch.

German very often forms compound nouns by joining smaller words into one larger noun.

Schwierigkeitsgrad is made up of:

• Schwierigkeit = difficulty
• Grad = degree / level

Together, Schwierigkeitsgrad means degree of difficulty or difficulty level.

This is completely normal in German. English often uses several words where German prefers one compound noun.

Because it is a noun, and in German all nouns are capitalized.

So in this sentence:

• Wir is capitalized because it begins the sentence.
• Schwierigkeitsgrad is capitalized because it is a noun.

This is a standard rule in German spelling.

Yes, that is also possible, but the nuance is slightly different.

• besprechen often suggests going through something together, sometimes in a practical or organized way.
• diskutieren often suggests discussing something, sometimes with more debate or exchange of opinions.

So both can work, but besprechen can sound a bit more neutral or goal-oriented in many contexts.