La servo estas tiel bona, ke ni decidas reveni al tiu restoracio venontan semajnon.

Tiel ... ke is a very common Esperanto pattern meaning so ... that.

So:

• La servo estas tiel bona, ke ...
  = The service is so good that ...

Here:

• tiel = so, to such a degree
• ke = that

It introduces a result clause: the service is so good that it causes us to decide to come back.

La is the definite article, meaning the.

So:

• la servo = the service

In this sentence, it refers to the specific service at that restaurant, not service in general. Esperanto uses la much like English uses the.

Compare:

• Servo estas grava. = Service is important.
  (service in general)
• La servo estas bona. = The service is good.
  (the specific service here)

Because bona is a predicate adjective after estas.

In Esperanto, adjectives take -n only when they are accusative, usually because they describe a direct object. But after esti (to be), the adjective does not take -n.

So:

• La servo estas bona. = The service is good.

Here:

• la servo is the subject
• bona describes the subject

That is why it stays bona, not bonan.

After decidi (to decide), Esperanto normally uses an infinitive if the same person does both actions.

So:

• ni decidas reveni = we decide to return

This works like English:

• We decide to return

Here:

• decidas = decide
• reveni = to return

Because we are both the ones deciding and the ones returning, the infinitive reveni is the natural form.

Decidas is the present tense form of decidi.

So literally the sentence says:

• The service is so good that we decide to return...

Esperanto often uses the present tense in a straightforward way, just like English can. Whether English translates it as decide or decided depends on context, but the Esperanto form here is clearly present.

If you wanted past tense, it would be:

• ni decidis reveni = we decided to return

So this sentence is describing the situation as happening now or in a present-style narration.

Because reveni often works with al when you mean return to a place.

So:

• reveni al la restoracio = return to the restaurant

The preposition al means to.

This is very similar to English:

• return to a place

Without al, the meaning would be incomplete or unnatural in this context.

Because the phrase is governed by the preposition al.

In Esperanto, prepositions usually replace the need for the accusative -n. So:

• al tiu restoracio = to that restaurant

Here:

• tiu = that
• restoracio = restaurant

Since al already marks the relationship (to), you do not also add -n.

A helpful rule:

• no -n after most prepositions
• unless there is some special reason, such as motion across/into something in certain expressions

But in this sentence, ordinary al tiu restoracio is correct.

Tiu means that, while ĉi tiu means this.

So:

• tiu restoracio = that restaurant
• ĉi tiu restoracio = this restaurant

In the sentence, tiu points to a particular restaurant already known in the context.

Esperanto also allows tiu ĉi, but ĉi tiu is more common in modern usage.

This is a very common Esperanto time expression.

Venontan semajnon means next week, and the -n marks time when.

So Esperanto often uses the accusative for expressions of time without a preposition:

• lundon = on Monday
• venontan semajnon = next week
• pasintjare or pasintan jaron = last year

In your sentence:

• venontan agrees with semajnon
• both are singular accusative

That is why both words have -n:

• venonta semajno = next week
• venontan semajnon = next week / during the next week / in the coming week

Yes. Venonta comes from veni (to come).

It is an active participle used adjectivally:

• veni = to come
• venonta = coming, upcoming

So:

• venonta semajno = the coming week / the upcoming week
• venontan semajnon = next week

This is very natural Esperanto. You will also see similar forms like:

• pasinta semajno = past week / last week
• sekva semajno = following week / next week

Yes, Esperanto word order is fairly flexible, although the original version is very natural.

The standard sentence:

• La servo estas tiel bona, ke ni decidas reveni al tiu restoracio venontan semajnon.

This is clear and neutral.

You could move some parts for emphasis, for example:

• Venontan semajnon ni decidas reveni al tiu restoracio.
• Al tiu restoracio ni decidas reveni venontan semajnon.

But the original order is probably the best for a learner because it sounds natural and easy to follow.

Yes. Restoracio is the standard modern word for restaurant.

You may also encounter manĝejo (eating place) in some contexts, but restoracio is the ordinary word you would expect in everyday Esperanto.

So in this sentence:

• tiu restoracio = that restaurant

is completely normal.