Op de linker trapper zit nog modder van het fietspad.

Dutch often puts a place expression first when it wants to set the scene.

• Op de linker trapper = On the left pedal
• Then comes the verb: zit
• Then the subject: nog modder van het fietspad

This is a normal Dutch word order pattern. Because the sentence starts with something other than the subject, the finite verb moves to the second position.

So:

• Op de linker trapper zit nog modder van het fietspad.
• More basic order: Er zit nog modder van het fietspad op de linker trapper.

Both are natural, but the original sentence emphasizes where the mud is.

Dutch often uses a positional verb where English would simply use to be.

Here, zitten is used because the mud is understood as stuck to or attached to the pedal.

So:

• Er is modder op de trapper = understandable, but less idiomatic
• Er zit modder op de trapper = more natural Dutch

A few common Dutch position verbs are:

• staan = stand
• liggen = lie
• zitten = sit / be attached / be located in or on something

With dirt, stickers, paint, buttons, handles, etc., Dutch often uses zitten.

Here nog means still.

So the sentence suggests that the mud is still there, perhaps after a ride or even after some cleaning.

• zit nog modder = there is still mud
• Without nog: Op de linker trapper zit modder = There is mud on the left pedal

So nog adds the idea of continuation: the mud has not gone away yet.

Dutch uses special attributive forms for left and right before nouns:

• de linker trapper = the left pedal
• de rechter trapper = the right pedal

By contrast:

• links and rechts are more often used adverbially or predicatively:
  • De trapper zit links. = The pedal is on the left.
  • Hij sloeg links af. = He turned left.

So before a noun, linker/rechter are the normal forms.

Because modder is usually an uncountable noun, like mud in English.

So Dutch normally says:

• er zit modder op
• not usually er zit een modder op

Just like in English, you usually do not say a mud.

If you want to specify a quantity, you could say something like:

• een beetje modder = a bit of mud
• veel modder = a lot of mud

Here van means from.

So:

• modder van het fietspad = mud from the bike path

It tells you the source of the mud.

This does not mean the mud belongs to the bike path in a possessive sense. It means the mud got onto the pedal from the bike path.

Dutch very often makes compound nouns by writing them as one word.

• fiets = bicycle
• pad = path
• fietspad = bicycle path / bike path

This is very normal in Dutch. English sometimes writes similar things as two words, but Dutch usually joins them.

Other examples:

• treinstation = train station
• huisdeur = front door / house door
• regenjas = raincoat

Yes. Trapper means pedal, especially a bicycle pedal.

In everyday Dutch, trapper is a very common word in cycling contexts.

You may also see pedaal, but trapper is especially natural for a bike pedal.

So:

• de linker trapper = the left pedal

Because trapper is a de-word.

In Dutch, every noun is either a de-word or a het-word:

• de trapper
• therefore op de linker trapper

You usually just have to learn the article with the noun.

Yes, very naturally:

• Er zit nog modder van het fietspad op de linker trapper.

This version starts with er, which often works like there in English existential sentences:

• There is still mud on the left pedal.

The original sentence puts the location first for emphasis:

• Op de linker trapper zit nog modder van het fietspad.

Both are good Dutch.

Normally, de linker trapper means the pedal on the bicycle’s left side, from the bicycle/rider’s natural perspective.

So if you are sitting on the bike, it is the pedal by your left foot.

That is usually how left/right is understood for vehicles, body parts, and paired objects.

It is neutral everyday Dutch.

Nothing in it is especially formal or especially casual. It would sound normal in conversation, in writing, or in a practical description of a bicycle.

You could map the words that way, but it would sound unnatural in English.

A natural English translation would be something like:

• There is still mud from the bike path on the left pedal.
• The left pedal still has mud from the bike path on it.

This is a good example of where Dutch and English use different normal sentence patterns, even though the meaning is straightforward.