הוא התנצל על מה שאמר, ואני החלטתי לסלוח לו.

A natural pronunciation is:

Hu hitnatzel al ma she'amar, va'ani hechlateti lisloach lo.

A slightly more phonetic version:

hoo heet-na-TSEL al ma she-a-MAR, va-a-NEE hech-la-TEE lis-LO-ach lo

A few stress points:

• התנצל → stress on the last syllable: hitnaTZEL
• אמר → stress on the last syllable: aMAR
• החלטתי → stress on the last syllable: hechlaTETI
• לסלוח → stress on the last syllable: lisLOach

התנצל means he apologized.

It is:

• past tense
• 3rd person masculine singular
• from the verb להתנצל = to apologize

So:

• הוא התנצל = he apologized

This verb is in the התפעל pattern, which often has a reflexive or self-directed sense. You do not need to translate that literally here, but it helps explain the form.

In Hebrew, להתנצל על... means to apologize for...

So:

• התנצל על מה שאמר = he apologized for what he said

This is just the normal preposition used with this verb.

More examples:

• היא התנצלה על הטעות = she apologized for the mistake
• התנצלתי על האיחור = I apologized for the delay

So English for here usually becomes Hebrew על.

מה שאמר literally means something like what he said or that which he said.

Breakdown:

• מה = what
• ש־ = that / which
• אמר = he said

Together:

• מה שאמר = what he said

This is a very common Hebrew structure.

Compare:

• אני זוכר מה שאמרת = I remember what you said
• זה מה שרציתי = this is what I wanted

Because Hebrew verbs usually already show the subject.

אמר by itself means he said.

So in:

• מה שאמר

the word אמר already tells you the subject is he:

• masculine
• singular
• past tense

If the speaker wanted she said, it would be:

• מה שאמרה = what she said

So Hebrew often does not need separate subject pronouns when the verb form already makes the subject clear.

Yes, it could.

• ואני החלטתי = and I decided
• והחלטתי = and decided / and I decided

Because החלטתי already means I decided, the word אני is not grammatically necessary.

So why include אני? Usually for:

• emphasis
• contrast
• a slightly more explicit subject shift

In this sentence, ואני can feel like:

• and I, for my part, decided to forgive him

So the pronoun is optional, but it adds a bit of emphasis.

החלטתי means I decided.

It is:

• past tense
• 1st person singular
• from להחליט = to decide

Hebrew often uses:

• החליט + infinitive to mean
• decided to + verb

So:

• החלטתי לסלוח = I decided to forgive

This is very similar to English:

• I decided to go
• I decided to stay
• I decided to forgive

Hebrew examples:

• החלטתי ללמוד = I decided to study
• הוא החליט לעזוב = he decided to leave

Because the verb לסלוח (to forgive) takes the preposition ל־ in Hebrew.

So Hebrew says:

• לסלוח לו = literally to forgive to him but naturally translated as
• to forgive him

This is one of those places where Hebrew and English use different verb patterns.

Examples:

• סלחתי לו = I forgave him
• היא סלחה לי = she forgave me
• נסלח להם = we will forgive them

So with סלח, use:

• לי = to me
• לך / לךְ = to you
• לו = to him
• לה = to her
• לנו = to us
• להם / להן = to them

לו means to him.

It is made of:

• ל־ = to
• ו = him

So:

• לסלוח לו = to forgive him
• literally: to forgive to him

Very common similar forms:

• לי = to me
• לך = to you (masculine)
• לךְ = to you (feminine)
• לה = to her
• לנו = to us

These short attached pronoun forms are extremely common in Hebrew.

The sentence as written is very natural:

• הוא התנצל על מה שאמר, ואני החלטתי לסלוח לו.

But Hebrew word order is somewhat flexible.

Possible variations include:

• הוא התנצל על מה שאמר, והחלטתי לסלוח לו.
• אני החלטתי לסלוח לו אחרי שהוא התנצל על מה שאמר.
• על מה שאמר הוא התנצל, ואני החלטתי לסלוח לו.
  (more marked or stylistic)

The original version is probably the most straightforward and natural for everyday Hebrew.

Yes. Hebrew gives you a few options depending on style and nuance.

For example:

• על מה שאמר = for what he said
• על הדברים שאמר = for the things he said
• על מה שהוא אמר = also for what he said, but slightly fuller

The version in your sentence, מה שאמר, is very normal and concise.

A small note:

• מה שאמר sounds natural and efficient
• מה שהוא אמר is also common, especially in speech
• הדברים שאמר sounds a bit more specific or explicit

It sounds neutral and natural.

The vocabulary is standard modern Hebrew:

• התנצל = standard
• החלטתי = standard
• לסלוח לו = standard

So this sentence would work well in:

• conversation
• writing
• study materials
• everyday narration

It is not slang, and it is not especially formal either.