אני לא יודעת מי החביא את המכתב, אבל ברור שמישהו ניסה להסתיר אותו.

Because the speaker is female. In Hebrew, present-tense forms agree with gender and number.

• אני לא יודעת = said by a woman
• אני לא יודע = said by a man

So this sentence specifically sounds like a female speaker.

Yes. In modern Hebrew, the present tense is built from forms that also behave like participles. That means they change for gender and number.

So יודעת is the feminine singular present form of לדעת = to know.

This is why Hebrew present tense can look a little different from English: it is not built with a separate word like do or a special ending like English know / knows.

Yes, it could. לא יודעת מי החביא את המכתב... would also be natural.

Hebrew often drops subject pronouns when the verb already makes the meaning clear. But speakers still use אני for clarity, emphasis, contrast, or just normal rhythm.

So:

• אני לא יודעת = fully explicit
• לא יודעת = also natural in conversation

את is the direct-object marker. It appears before a definite direct object.

It does not have a separate meaning in English, so usually you do not translate it.

Here:

• המכתב = the letter
• because it is definite, Hebrew uses את
• החביא את המכתב = hid the letter

If the object were indefinite, you would usually not use את:

• החביא מכתב = hid a letter

The prefix ה־ is the Hebrew definite article, meaning the.

So:

• מכתב = a letter / letter
• המכתב = the letter

This matters grammatically because definite direct objects usually require את before them. That is why you get את המכתב together.

With מי = who, Hebrew often uses third-person masculine singular as the default when the person is unknown or unspecified, especially in past tense questions.

So מי החביא את המכתב is a very normal way to say who hid the letter?

If the speaker knew or assumed the person was female, they might say:

• מי החביאה את המכתב

But the masculine singular form is often used as the neutral default.

They are close in meaning, but not identical.

• החביא = hid, often with the sense of putting something out of sight
• להסתיר = to conceal / to hide

In everyday Hebrew, these can overlap a lot. Here the sentence uses one form for the completed action being asked about, and another after ניסה = tried.

So the distinction is not huge, but there is a slight nuance:

• החביא focuses on the act of hiding the letter
• להסתיר focuses on keeping it concealed

You could also hear מישהו ניסה להחביא אותו, and that would also make sense.

Hebrew usually does not use a present-tense form of to be.

So:

• ברור literally means clear
• ברור ש... means it is clear that...

Hebrew does not need a separate word for it is here.

So the structure is very natural:

• ברור שמישהו ניסה... = It’s clear that someone tried...

ש־ means that.

It is attached directly to the next word, so:

• ש + מישהו = שמישהו

This is very common in Hebrew. So:

• ברור שמישהו ניסה... = It is clear that someone tried...

You can think of ש־ as a short attached version of that.

After verbs like ניסה = tried, Hebrew usually uses an infinitive with ל־.

So:

• ניסה = tried
• להסתיר = to hide / to conceal

Together:

• ניסה להסתיר = tried to hide

This works much like English: tried to hide, not tried hid.

מישהו is the standard word for someone / somebody, and grammatically it is masculine.

Hebrew often uses masculine forms as the default when gender is unknown or unspecified.

If you specifically meant some woman / some girl, you would usually say:

• מישהי

Because this sentence says מישהו, the following verb is also masculine singular:

• מישהו ניסה

אותו refers to המכתב.

Since מכתב is masculine singular, the object pronoun is also masculine singular:

• אותו = him / it as a masculine singular direct object

So here it means it, referring to the letter.

Compare:

• המכתב ... אותו = masculine singular
• ההודעה ... אותה = feminine singular

Yes, Hebrew word order is somewhat flexible, but this sentence is very natural and standard.

The basic flow is:

• אני לא יודעת
• מי החביא את המכתב
• אבל ברור שמישהו ניסה להסתיר אותו

A speaker could move parts around for emphasis, but the version here sounds neutral and natural. It is a good model sentence for everyday Hebrew.