ajimi o shitara aji ga tarinakatta node, haha ni mou sukoshi shio o irete hoshii to tanonda.

It breaks into two main parts:

1. 味見をしたら味が足りなかったので = When/after I tasted it, the flavor was not strong enough, so...

2. 母にもう少し塩を入れてほしいと頼んだ = I asked my mother to add a little more salt.

So the full flow is:

After tasting it, I found it needed more flavor, so I asked my mother to add a little more salt.

味見 is a noun meaning taste-testing or sampling the taste.
Japanese often makes verbs by combining a noun with する, so:

• 味見する = to taste-test
• 味見をする = same meaning, just with を

In this sentence, 味見をしたら means when I tasted it or after I tasted it.

Here, 〜たら means when or after doing something.

So 味見をしたら means:

• when I tasted it
• after I tasted it

It is not really a hypothetical if here. The speaker actually did the tasting, and then discovered the problem.

Literally, 味が足りない means the flavor is insufficient or the taste is lacking.

In natural English, that usually becomes something like:

• it didn’t have enough flavor
• it was under-seasoned
• it needed more seasoning

So this does not mean the speaker wanted more kinds of taste. It means the dish tasted weak or incomplete.

が marks 味 as the thing that is insufficient.

So the sentence is focusing on what was lacking:
the flavor was not enough.

If you used 味は, it would sound more contrastive, like:

• As for the flavor, it was lacking...

But 味が足りなかった is the more straightforward way to say the flavor was insufficient.

ので and から can both mean because, but ので is usually a bit softer and more explanatory.

• 足りなかったので = because it wasn’t enough / since it was lacking

Compared with から, ので often sounds a little more neutral and less blunt. In a sentence like this, it fits naturally because the speaker is calmly explaining the reason for asking.

もう少し means a little more.

In this sentence:

• もう少し塩を入れて = add a little more salt

It modifies the amount of salt being added.
So the speaker is not asking for a big change, just a small extra amount.

〜てほしい means want someone to do something.

So:

• 塩を入れてほしい = (I) want someone to add salt

More specifically here, because of 母に, it means:

• I want my mother to add salt

This pattern is very common:

• 友だちに来てほしい = I want my friend to come
• 先生に見てほしい = I want the teacher to look at it

So 入れてほしい is not just a general desire. It means the speaker wants another person to do the action.

This pattern is:

• person に
• request content と
• 頼む

So:

• 母に = to my mother
• もう少し塩を入れてほしいと = that I wanted her to add a little more salt
• 頼んだ = asked/requested

Together, it means:

I asked my mother to add a little more salt.

The と marks the content of what was said or requested.

Both kinds of expressions exist, but 〜てほしいと頼む clearly expresses the speaker’s desire for someone to do the action.

So:

• 塩を入れてほしいと頼んだ = I asked that she add salt / I asked her to add salt

It is a very natural reported-speech way to describe a request.

A more direct quotation could also be something like:

• もう少し塩を入れて、と頼んだ
• もう少し塩を入れてください、と頼んだ

But 〜てほしいと頼んだ sounds smooth and indirect in narration.

The subject is omitted because Japanese often leaves it out when it is clear from context.

Here, the understood subject is most naturally I:

• (I) tasted it
• (I) found the flavor lacking
• (I) asked my mother...

This is very normal in Japanese. If the sentence explicitly said 私は, it would still be correct, but it is not necessary.

Yes, 味 is natural. It is broad and simply refers to the overall flavor.

So 味が足りない can mean:

• the dish is bland
• the seasoning is weak
• the flavor is not strong enough

A more specific word like 塩気 would focus only on saltiness, but 味 lets the speaker first say the flavor was lacking overall, and then explain the solution: add a little more salt.

Because 塩 is the direct object of 入れる.

• 塩を入れる = to add salt

So in もう少し塩を入れてほしい, the thing the speaker wants added is salt, which is why it takes を.