ano sizukana kafe de tomodati to issyo ni nihongo wo rensyuusimasen ka.

Here, あの means that, as in that quiet café.

It is not the hesitation filler あの… meaning um... In this sentence, it directly modifies the noun phrase:

• あの カフェ = that café
• あの 静かな カフェ = that quiet café

It suggests both speaker and listener can identify which café is being talked about.

静か is a な-adjective, not an い-adjective.

When a な-adjective comes before a noun, you add な:

• 静か = quiet
• 静かな カフェ = a quiet café

Compare:

• きれいな 部屋 = a clean / pretty room
• 便利な 場所 = a convenient place

So 静かなカフェ is the correct form because the adjective is directly modifying カフェ.

The particle で marks the place where an action happens.

In this sentence, the action is practicing Japanese, and the place where that happens is the café:

• カフェで = at the café

This is different from に, which often marks a destination, time, or existence in some contexts.

For example:

• カフェで 勉強します = study at a café
• カフェに 行きます = go to a café

So で is used because the café is the location of the action.

Yes, they overlap in meaning, but they are often used together naturally.

• 友達と = with a friend / with friends
• 一緒に = together

So:

• 友達と一緒に = together with a friend / with friends together

Using both makes the idea of doing something jointly very clear and natural.

You could sometimes say just:

• 友達と日本語を練習しませんか。

That would still make sense. Adding 一緒に gives a stronger let’s do this together feeling.

In 一緒に, the に helps turn 一緒 into an adverbial expression meaning together.

So:

• 一緒 = togetherness / same company
• 一緒に = together

It works like an adverb describing how the action is done:

• 一緒に行きます = go together
• 一緒に食べましょう = let’s eat together

In your sentence, 友達と一緒に describes the manner/company of practicing.

The particle を marks the direct object of the verb.

Here, the thing being practiced is Japanese:

• 日本語を練習する = to practice Japanese

So 日本語 is the object of 練習する, which is why it takes を.

Similar examples:

• 英語を勉強します = study English
• ピアノを練習します = practice piano

This is a very common Japanese pattern.

• 練習する = to practice
• 練習しません = do not practice / will not practice
• 練習しませんか = won’t you practice...? / would you like to practice...?

Even though it uses the negative form, ～ませんか is often used to make a polite invitation or suggestion.

So it does not usually sound like a real negative question in English. It is more like:

• Would you like to practice Japanese...?
• Won’t you practice Japanese...?
• How about practicing Japanese...?

This is softer and more inviting than a plain question.

They have different functions.

• 練習しますか = Will you practice? / Do you practice?
  • This is more of a straightforward question.
• 練習しませんか = Won’t you practice? / Would you like to practice?
  • This is commonly used as an invitation.

So if you want to invite someone, ～ませんか is much more natural.

Compare:

• 一緒に映画を見ますか。 = Will you watch a movie together? / Do you watch movies together?
• 一緒に映画を見ませんか。 = Would you like to watch a movie together?

The second one sounds more like an invitation.

Yes. 友達 can refer to:

• a friend
• friends

Japanese nouns usually do not have a required singular/plural distinction the way English does. Context tells you which is meant.

So 友達と一緒に could mean:

• together with a friend
• together with friends

If the meaning shown to the learner uses a friend, that is a very reasonable interpretation.

Yes, from an English point of view, the subject is omitted.

Japanese often leaves out subjects when they are clear from context. In an invitation with ～ませんか, the implied meaning is usually something like:

• Would you like to ... ?
• Shall we ... ?
• Won’t we / won’t you ... ?

So the sentence does not need to explicitly say you or we.

That omission is very normal in Japanese.

Some parts are fixed, and some are flexible.

Fixed or tightly connected parts

These should stay together:

• あの 静かな カフェ = that quiet café
• 友達と 一緒に = together with a friend
• 日本語を 練習しませんか = won’t you practice Japanese?

More flexible parts

Because particles show each word’s role, Japanese word order is more flexible than English. For example, you could also say:

• 友達と一緒に、あの静かなカフェで日本語を練習しませんか。

That still sounds natural.

But the verb typically comes at the end, so 練習しませんか should stay last.

No, normal Japanese is usually written without spaces.

A standard version would look like this:

• あの静かなカフェで友達と一緒に日本語を練習しませんか。

Spaces are often added in beginner materials to help learners see the parts more clearly. So the spacing here is for learning purposes, not standard everyday writing.

Yes.

Without あの, it would become more general:

• 静かなカフェで友達と一緒に日本語を練習しませんか。 = Would you like to practice Japanese together with a friend at a quiet café?

With あの, it points to a specific café already known to both people:

• あの静かなカフェ = that quiet café

So あの adds specificity.

Yes, it can be.

• 日本語を練習する = practice Japanese

This is natural, especially when talking about actively using the language, such as speaking, conversation practice, pronunciation, or drills.

Depending on context, Japanese learners may also often hear:

• 日本語を勉強する = study Japanese

A rough difference is:

• 勉強する = study, learn
• 練習する = practice

So 練習する fits well when the focus is on actually using what you know.

Yes, it sounds polite and friendly.

The politeness comes mainly from:

• しませんか rather than a plain casual form like しない？

Compare:

• 日本語を練習しませんか。 = polite
• 日本語を練習しない？ = casual

So this sentence would work well in a polite conversation, especially with someone you are not extremely close to.