Ten list jest napisany po polsku.

A word-for-word breakdown is:

• ten = this
• list = letter
• jest = is
• napisany = written
• po polsku = in Polish

So the whole sentence is literally This letter is written in Polish.

This is a false friend.

In Polish, list means letter, as in something you send by post or sometimes a written message.

If you want the English meaning of list, the Polish word is usually lista.

So:

• list = letter
• lista = list

Because ten has to agree with list.

The noun list is:

• masculine
• singular
• nominative here, because it is the subject of the sentence

So the demonstrative must also be masculine singular nominative:

• ten list = this letter

Compare:

• ten list = masculine
• ta książka = feminine
• to okno = neuter

Usually, in sentences like this, ten is translated as this.

However, in real usage, Polish ten can sometimes be closer to English that, depending on context, emphasis, and what has already been mentioned.

So in beginner-level translation:

• ten list = this letter

But in natural speech, the exact English choice can depend on context.

Napisany is a participle meaning written, and it comes from the verb napisać, which means to write or to write down in a completed sense.

It has the ending -y because it agrees with list, which is masculine singular nominative.

Compare the agreement:

• ten list jest napisany = masculine singular
• ta książka jest napisana = feminine singular
• to zdanie jest napisane = neuter singular

So napisany changes its form just like an adjective would.

It is basically a passive-style structure:

• jest = is
• napisany = written

So jest napisany means is written.

Because napisany comes from the perfective verb napisać, it can also suggest a resulting state, something like:

• has been written
• is written
• is in a written form

In this sentence, the natural English translation is simply is written in Polish.

Not in normal standard Polish here.

Polish often drops subject pronouns, but it does not usually drop the finite verb to be in a sentence like this.

So:

• Ten list jest napisany po polsku = correct
• Ten list napisany po polsku = sounds incomplete in ordinary speech, though it might appear in notes, headlines, or very compressed style

For a full normal sentence, keep jest.

Because this is the standard Polish way to talk about languages.

Polish normally uses:

• po polsku = in Polish
• po angielsku = in English
• po niemiecku = in German

So after many verbs and expressions involving language, po + language form is the usual pattern.

A more formal alternative is:

• w języku polskim = in the Polish language

But po polsku is the everyday, natural expression.

Because w polskim by itself does not mean in Polish when talking about language.

If you want to say in Polish as a language, the normal form is:

• po polsku

If you say w polskim, it sounds incomplete, because polskim is just an adjective form meaning something like in the Polish ... and it needs a noun after it, for example:

• w polskim domu = in the Polish house
• w polskim języku = in the Polish language

So for languages, learn po polsku as a fixed phrase.

Because in Polish, names of languages and adjectives derived from countries or nationalities are usually written with a lower-case letter.

So Polish writes:

• po polsku
• język polski
• angielski
• niemiecki

This is different from English, where Polish and English are capitalized.

For a beginner, the best approach is to learn po polsku as a whole expression.

Grammatically, polsku is an old case form used after po. Historically it is related to the locative pattern, but in modern learning practice it is easiest to treat expressions like these as set language forms:

• po polsku
• po angielsku
• po francusku

You do not usually build them freely the same way you build ordinary adjective phrases.

Yes, Polish word order is more flexible than English.

The neutral order here is:

• Ten list jest napisany po polsku.

But other orders are possible for emphasis, for example:

• Po polsku jest napisany ten list.

That might emphasize in Polish.

Even so, the original version is the most natural and neutral for a learner to use first.