Bei schwierigen Sätzen zähle ich die Silben langsam und achte auf jeden Vokal.

Because bei takes the dative case.

• bei = a preposition that is followed by dative
• Sätzen is the dative plural of Sätze
• The adjective schwierig also has to take a dative plural ending, so it becomes schwierigen

So:

• nominative plural: schwierige Sätze
• dative plural: bei schwierigen Sätzen

That is why both words change.

This is because the base noun is der Satz, and its plural is die Sätze.

In the sentence, though, the noun is not just plural, but dative plural because of bei. For many nouns in the dative plural, German adds -n if possible.

So the steps are:

• singular: der Satz
• plural: die Sätze
• dative plural: den Sätzen or after a preposition, just bei Sätzen

So Sätzen shows:

• the normal plural change: a → ä
• the dative plural ending: -n

Here bei means something like when dealing with, in the case of, or with.

So Bei schwierigen Sätzen means:

• with difficult sentences
• when working with difficult sentences
• in difficult sentences is possible in some contexts, but here with difficult sentences is the most natural understanding

It does not literally mean physical location here, even though bei often can mean at or near in other sentences.

Because German main clauses follow the verb-second rule.

That means the finite verb must come in the second slot, not necessarily the second word.

In this sentence:

1. Bei schwierigen Sätzen = first slot
2. zähle = finite verb in second position
3. ich = subject comes after the verb

So the structure is:

• Bei schwierigen Sätzen | zähle | ich ...

This is very common in German. If you begin with something other than the subject, the subject usually moves after the verb.

Yes. That is also correct.

German allows different elements to come first in a main clause. Compare:

• Ich zähle bei schwierigen Sätzen die Silben langsam ...
• Bei schwierigen Sätzen zähle ich die Silben langsam ...

Both are grammatical. The version with Bei schwierigen Sätzen first puts more emphasis on the situation or context.

Because Silben is the plural of die Silbe, and here it is the direct object of zählen.

The verb zählen usually takes an accusative object:

• Ich zähle die Silben.
• Sie zählt die Fehler.

Since Silben is plural, the article is die in both nominative and accusative plural. So the form is:

• singular: die Silbe
• plural: die Silben
• accusative plural: die Silben

Because langsam is an adverb, and German word order with adverbs is flexible but follows common patterns.

Here, die Silben is the object, and langsam describes how the speaker counts them. So:

• zähle ich die Silben langsam

sounds natural and clear.

You could also sometimes move adverbs around for emphasis, but this version is very normal. The sentence keeps the object close to the verb and then adds the manner adverb langsam.

achten auf is a fixed verb-preposition combination meaning to pay attention to.

Important points:

• the basic verb is achten
• it combines with auf
• auf here is not a separable prefix
• the noun after auf is in the accusative

So:

• Ich achte auf den Ton.
• Wir achten auf die Details.
• Sie achtet auf jeden Vokal.

You should learn achten auf + accusative as a chunk.

Because auf in achten auf requires the accusative case, and Vokal is masculine: der Vokal.

So the accusative masculine forms are:

• jeder Vokal = nominative
• jeden Vokal = accusative

That is why both words show accusative masculine endings:

• jeden = accusative masculine form of jeder
• Vokal stays the same as a noun, but its article/determiner changes

jeden Vokal means each vowel or every vowel. It emphasizes individual attention to one vowel at a time.

Compare:

• auf jeden Vokal achten = pay attention to each vowel individually
• auf alle Vokale achten = pay attention to all vowels

Both are possible, but jeden Vokal sounds especially focused and careful.

Because in German, all nouns are capitalized.

So in this sentence:

• Sätzen is a noun
• Silben is a noun
• Vokal is a noun

That is standard German spelling. Adjectives and verbs are normally not capitalized unless they begin the sentence or are part of a noun phrase used as a noun.

Yes. der Vokal is the standard grammatical/linguistic word for vowel.

Another very common German word is der Selbstlaut, but that is less common in everyday modern usage and may sound more traditional or school-like.

So for most learners, Vokal is the main word to remember.

Very roughly, the structure is:

• Bei schwierigen Sätzen = with difficult sentences / when dealing with difficult sentences
• zähle ich = count I
• die Silben = the syllables
• langsam = slowly
• und achte auf = and pay attention to
• jeden Vokal = each vowel

So a very literal gloss would be:

With difficult sentences, count I the syllables slowly and pay attention to each vowel.

That is not natural English, but it helps show the German structure.

Yes, a few common ones:

• schwierigen: the beginning schw- can be tricky; sch sounds like sh
• Sätzen: the ä is different from plain a
• zähle: the ä again matters here
• Silben: the i is short
• achte: ch is the soft sound heard after front vowels, not like English k
• Vokal: stress is on the second syllable: vo-KAL

A rough stress pattern is:

• bei SCHWIErigen SÄTzen
• ZÄHle ich die SILben LANGsam
• und ACHte auf JEden vo-KAL

The dictionary forms are:

• zählen = to count
• achten auf = to pay attention to

In the sentence, they appear as:

• zähle = I count
• achte = I pay attention

Both are in the present tense, first person singular:

• ich zähle
• ich achte