अगर तुम सच बोलोगी, तो मैं खुश रहूँगी।

That is normal in Hindi.

In Hindi, a future condition often uses the future tense in both parts:

• अगर तुम सच बोलोगी = if you tell / if you will tell the truth
• तो मैं खुश रहूँगी = then I will be happy

So the Hindi structure is more literally like If you will speak the truth, then I will stay happy, but the natural English translation is If you tell the truth, I’ll be happy.

They work like if ... then ...

• अगर = if
• तो = then

So:

• अगर तुम सच बोलोगी, तो मैं खुश रहूँगी। = If you tell the truth, then I will be happy.

In everyday Hindi, तो is often optional:

• अगर तुम सच बोलोगी, मैं खुश रहूँगी।

You may also hear the condition expressed without अगर, especially in speech:

• तुम सच बोलोगी तो मैं खुश रहूँगी।

But for learners, अगर ... तो ... is a very clear pattern.

Because both verbs are agreeing with feminine singular subjects in the future tense.

• तुम ... बोलोगी = you (female) will speak
• मैं ... रहूँगी = I (female speaker) will remain/be

So the sentence suggests:

• the person being addressed is female
• the speaker is also female

Hindi verbs often show gender in this way.

Only the verb forms would change.

• To a male addressee, from a female speaker:
  अगर तुम सच बोलोगे, तो मैं खुश रहूँगी।

• To a female addressee, from a male speaker:
  अगर तुम सच बोलोगी, तो मैं खुश रहूँगा।

• To a male addressee, from a male speaker:
  अगर तुम सच बोलोगे, तो मैं खुश रहूँगा।

So:

• -गी = feminine singular
• -गा = masculine singular
• -गे = masculine/plural/respectful in many contexts

सच means truth, and सच बोलना is a very common expression meaning to tell the truth or to speak the truth.

So:

• सच बोलोगी = you will tell the truth

Hindi often uses बोलना in expressions with सच and झूठ:

• सच बोलना = to tell the truth
• झूठ बोलना = to tell a lie / lie

You can also say सच कहना in some contexts, but सच बोलना is extremely common and natural.

Because Hindi does not have articles like a, an, and the.

So सच can mean:

• truth
• the truth

The exact meaning comes from context.

That is why सच बोलना naturally means to tell the truth, even though there is no separate word for the.

Yes—रहना literally means to stay, to remain, or to live. Here it gives the idea of remaining in a state.

So:

• खुश रहूँगी literally = I will remain happy
• natural English = I will be happy

Hindi often uses adjective + रहना to describe continuing in a state:

• चुप रहना = to stay quiet
• तैयार रहना = to stay ready
• खुश रहना = to stay/be happy

If you said खुश होऊँगी, that would lean more toward I will become happy.
खुश रहूँगी focuses more on the state of being happy.

The overall pattern is:

• अगर + condition, तो + result

Inside each clause, Hindi usually follows subject-object-verb order.

So:

• तुम सच बोलोगी

  • तुम = you
  • सच = truth
  • बोलोगी = will speak / will tell

• मैं खुश रहूँगी

  • मैं = I
  • खुश = happy
  • रहूँगी = will remain/be

A very literal breakdown is:

• If you truth will-speak, then I happy will-remain.

That sounds odd in English, but it is normal Hindi structure.

तुम is the common informal but not extremely rude word for you. It can be used with friends, family, children, classmates, partners, and many everyday situations.

Hindi has three common levels:

• तू = very intimate / very casual / sometimes rude
• तुम = informal, normal
• आप = polite, formal, respectful

If you wanted a polite version, you could say:

• अगर आप सच बोलेंगी, तो मैं खुश रहूँगी।
  (to a female addressee)

or

• अगर आप सच बोलेंगे, तो मैं खुश रहूँगा/रहूँगी।
  (to a male or mixed/formal addressee, depending on speaker gender)

Often, yes.

Hindi frequently leaves out pronouns when the context is clear, because the verb endings already give useful information.

For example:

• अगर सच बोलोगी, तो खुश रहूँगी।
• अगर तुम सच बोलोगी, खुश रहूँगी।

Both can be understood in the right context.

And as mentioned earlier, तो is often optional.

Still, the full version:

• अगर तुम सच बोलोगी, तो मैं खुश रहूँगी।

is very clear and is a good form for learners.

It is commonly transliterated as rahū̃gī.

A rough pronunciation guide is:

• र = light r
• हूँ = something like hoon, but with nasalization
• गी = gee

So roughly: ra-HOON-gee, with the oo sound slightly nasal.

The nasalization comes from ँ in हूँ.

So:

• रहूँगी ≈ rah-hoon-gee
  but with a nasalized hoon

Yes, that is the most natural reading.

Because of the verb endings:

• बोलोगी → the listener is female
• रहूँगी → the speaker is female

So this sentence is best understood as:

• a female speaker
• speaking to a female listener

Hindi often gives you this kind of information directly through verb agreement.