nihongo de atarasii kotoba wo oboeru tabi ni, sukosi zisin ga tukimasu.

Here, で marks the language or means used for the action.

So 日本語で means something like:

• in Japanese
• using Japanese

In this sentence, it connects to 覚える and tells you the learning is happening in/through Japanese.

A useful comparison:

• 日本語を勉強します = I study Japanese.
• 日本語で話します = I speak in Japanese.

So 日本語で is not the object of learning; it tells you the language context for the learning.

Usually, yes, that is how many learners will understand it in context: learning new words in Japanese.

But grammatically, 日本語で literally means in Japanese / using Japanese, so the phrase is a little less direct than saying:

• 日本語の新しい言葉
• 日本語の単語

Those versions make it clearer that the words themselves are Japanese words.

So this sentence is natural, but if someone wants to be very explicit, they might use 日本語の instead of 日本語で.

Because verb dictionary form + たびに is the normal pattern.

So:

• 覚えるたびに = every time I learn / whenever I learn

The dictionary form here does not mean only future tense. In Japanese grammar, the dictionary form is often used in patterns like this to describe a repeated action in general.

Other examples:

• 見るたびに = every time I see it
• 行くたびに = every time I go
• 聞くたびに = every time I hear it

たびに means every time or whenever, with the idea that something happens repeatedly.

So:

• 覚えるたびに、少し自信がつきます。 = Every time I learn one, I gain a little confidence.

By contrast, とき just means when or at the time and does not by itself emphasize repetition.

Compare:

• 覚えるとき = when I learn
• 覚えるたびに = every time I learn

So たびに is the better choice when you want the meaning each time this happens, this result follows.

The comma separates the time/condition clause from the main clause:

• 日本語で新しい言葉を覚えるたびに、
• 少し自信がつきます。

It works a lot like a pause in English after a long introductory phrase:

• Every time I learn a new word in Japanese, I gain a little confidence.

In Japanese, commas are often used for readability and natural pacing. In some cases, the sentence could still be understood without the comma, but using one here is very normal.

Because つく is an intransitive verb here.

In this expression, 自信がつく means:

• confidence develops
• confidence comes
• I gain confidence

With intransitive verbs, the thing that appears or develops is often marked with が, so:

• 自信がつく = confidence builds / I gain confidence

If you use the transitive partner つける, then you get:

• 自信をつける = to build confidence / to give oneself confidence

So:

• 自信がつきます = confidence comes/builds
• 自信をつけます = I build confidence

Both are possible in Japanese, but this sentence uses the intransitive pattern.

That is a very common question. つく has several meanings in Japanese, and this is one of them.

In 自信がつく, つく means something like:

• to be acquired
• to develop
• to come naturally over time

So 自信がつく is a set expression meaning:

• to gain confidence
• to become more confident

Japanese has many verbs like this that have a broad range of meanings depending on the noun they are used with.

少し means a little.

Here it modifies the main result:

• 少し自信がつきます = I gain a little confidence = I become a little more confident

It softens the statement and makes it sound natural and modest. The speaker is not saying they suddenly become fully confident—just that each time, their confidence increases a bit.

Because Japanese often leaves out the subject when it is already understood from context.

In English, you usually need to say I:

• Every time I learn a new word...

In Japanese, if it is obvious who is talking about themselves, 私は is often omitted.

So the full version could be:

• 私は、日本語で新しい言葉を覚えるたびに、少し自信がつきます。

But in natural Japanese, leaving out 私は is very common and sounds less repetitive.

Because つきます is the polite form.

• つく = plain/casual
• つきます = polite

So the sentence is written in a polite style, which is common in textbooks, conversations with strangers, formal situations, or careful speech.

A casual version would be:

• 日本語で新しい言葉を覚えるたびに、少し自信がつく。

The meaning is the same; only the level of politeness changes.

Both can refer to words, but they are not exactly the same.

• 言葉 = word(s), expression(s), language; broader and softer
• 単語 = vocabulary word, lexical item; more technical and study-focused

In this sentence, 言葉 sounds natural and general. It can feel a little more personal or less technical than 単語.

If you are specifically talking about memorizing vocabulary items from study materials, 単語 would also be very natural:

• 日本語で新しい単語を覚えるたびに、少し自信がつきます。

That version sounds a bit more like every time I memorize a new vocabulary word.