zititai ga kisoku wo kimemasu.

It is read:

じちたい が きそく を きめます。

Word by word:

• 自治体 = じちたい
• が
• 規則 = きそく
• を
• 決めます = きめます

They are particles, which show the role of each noun in the sentence.

• が marks the subject: the thing doing the action
  
  • 自治体が = the local government / municipality is the one acting
• を marks the direct object: the thing affected by the action
  
  • 規則を = rules/regulations are what gets decided

So the structure is basically:

[subject] が [object] を [verb]

Because Japanese normally puts the verb at the end of the sentence.

So while English says:

• The municipality decides rules.

Japanese is structured more like:

• Municipality subject-marker rules object-marker decides.

This is one of the most important sentence patterns in Japanese.

Both can mark something important in the sentence, but they do different jobs.

• が marks the subject
• は marks the topic

In a simple sentence like this, が is a natural way to identify who is doing the deciding.

• 自治体が規則を決めます。
  = The municipality decides the rules. / It is the municipality that decides the rules.

If you said:

• 自治体は規則を決めます。

that would feel more like:

• As for the municipality, it decides the rules
• or it could imply contrast, depending on context

So が is a straightforward subject marker here.

The dictionary form is 決める.

• 決める = plain form
• 決めます = polite -ます form

So:

• 決める is what you would find in a dictionary
• 決めます is what you use in polite speech

決める is a transitive verb, meaning it takes a direct object.

Here:

• 規則を決めます = decide the rules

A very useful comparison is:

• 決める = to decide something
• 決まる = to be decided

For example:

• 自治体が規則を決めます。 = The municipality decides the rules.
• 規則が決まります。 = The rules are decided / get decided.

This difference is very important in Japanese.

Japanese nouns usually do not show singular vs. plural clearly unless the context makes it clear.

So 自治体 could mean:

• a municipality
• the municipality
• municipalities
• local government(s)

The exact number depends on context and translation choice.

Japanese does not have articles like English a, an, or the.

So 自治体 does not by itself tell you:

• a municipality
• the municipality

And 規則 does not by itself tell you:

• a rule
• the rules
• rules

Context decides that.

This is very normal in Japanese, and learners gradually get used to filling that in from the situation.

They are similar, but not exactly the same.

• 規則（きそく） often sounds more formal and official
  • regulations
  • rules
  • provisions
• ルール is the borrowed word from English rule
  • often used for everyday rules, game rules, social rules, etc.

Because 自治体 is an official organization, 規則 fits very naturally here.

Yes, it is polite-neutral because of 決めます.

• 決めます is polite
• It is suitable for normal conversation, explanations, and written educational examples

A less polite/plain version would be:

• 自治体が規則を決める。

That form is common in:

• dictionary entries
• casual speech
• written explanations
• headlines or more direct written style

In some casual spoken Japanese, particles are sometimes dropped, but in a sentence like this, especially in a textbook or clear statement, they should stay.

• Standard: 自治体が規則を決めます。

If you remove the particles, the sentence becomes much less clear, especially for learners.

So for this kind of sentence:

• keep が
• keep を

They clearly show who does the action and what is being decided.

Breaking the kanji down can help memory:

自治体（じちたい）

• 自 = self
• 治 = govern
• 体 = body / entity

Together, 自治体 refers to a self-governing body, so in practice:
municipality / local government

規則（きそく）

• 規 = standard / rule
• 則 = rule / law / principle

Together, it means:

• rule
• regulation

You do not need to memorize every kanji meaning to use the word, but it can help you remember it.