mainiti tomodati to nihongo de hanasu to, motto sizen ni hanaseru you ni narimasu.

毎日 means every day, and it works as a time expression. In Japanese, time expressions often come near the beginning of the sentence, before the main action.

So:

• 毎日 友達と日本語で話す
  = talk with friends in Japanese every day

You could move 毎日 to another position in some cases, but putting it first is very common and natural.

The particle と here means with.

• 友達と話す = talk with friends

So 友達と tells you who you are speaking with.

Be careful: と can mean different things in different sentences, such as and or a conditional if/when, but after a noun like 友達, it often means with.

The particle で here marks the language or means used to do something.

• 日本語で話す = speak in Japanese
• 英語で書く = write in English

So 日本語で means the speaking is being done using Japanese.

When と is used as a conditional, the verb before it usually appears in the dictionary/plain form.

• 話すと = if/when (you) speak
• 行くと = if/when (you) go

So in this sentence:

• 毎日友達と日本語で話すと
  = if/when you speak Japanese with friends every day

This と often describes a natural result, regular result, or something that happens automatically.

This と is a conditional particle meaning something like if, when, or whenever.

In this sentence, it connects the habit/action with its result:

• 毎日友達と日本語で話すと、もっと自然に話せるようになります。
• If/when you speak Japanese with friends every day, you become able to speak more naturally.

This use of と often sounds like:

• a general truth
• a natural consequence
• a repeated result

It is less about a one-time choice and more about what normally happens.

もっと means more.

Here it modifies 自然に:

• もっと自然に話せる = can speak more naturally

It compares your future speaking ability to your current level. The idea is that by doing this regularly, your Japanese will sound more natural than before.

自然 means natural.
Adding に turns it into an adverb-like form:

• 自然に = naturally

So:

• 自然に話す = speak naturally
• もっと自然に話せる = be able to speak more naturally

This に is common with na-adjectives when they modify a verb.

話せる is the potential form of 話す, meaning can speak or be able to speak.

• 話す = speak
• 話せる = can speak

So:

• 自然に話せる = can speak naturally
• もっと自然に話せる = can speak more naturally

The sentence is not just saying you speak more naturally, but that you become able to do so.

ようになる is a very common pattern meaning:

• come to be able to...
• come to...
• reach the point where...

In this sentence:

• 話せるようになる = become able to speak
• もっと自然に話せるようになる = become able to speak more naturally

So ようになります shows a change over time. It means your ability improves gradually.

Both could work, but they focus on different things.

• 話せるようになる emphasizes becoming able to do something
• 上手になる emphasizes becoming skillful/good at something

So:

• もっと自然に話せるようになる = you develop the ability to speak more naturally
• 日本語が上手になる = your Japanese gets better

The sentence chooses 話せるようになる because it directly connects to the action of speaking.

Japanese often mixes a plain verb in one clause with a polite verb at the end of the sentence.

Here:

• 話すと is inside the conditional clause
• なります is the main sentence ending

The politeness level is usually determined by the final verb of the sentence. So ending with なります makes the whole sentence polite.

This is completely normal Japanese.

Yes. Japanese often omits the subject when it is understood from context.

So this sentence could mean:

• If you speak Japanese with friends every day, you’ll become able to speak more naturally.
• or in another context, I / someone could be understood

Japanese does not always need to say you, I, or people explicitly if the meaning is already clear.

The sentence breaks down like this:

• 毎日 = every day
• 友達と = with friends
• 日本語で = in Japanese
• 話すと = if/when you speak
• もっと = more
• 自然に = naturally
• 話せるようになります = become able to speak

So the structure is:

[habit/action] + と + [result]

More specifically:

If/when [you talk with friends in Japanese every day], [you become able to speak more naturally].

This is a very common and useful pattern in Japanese.