もう meaning in "もう腹ペコだ" I can not understand very well the meaning of in "". Looking online, the majority of the traslations say that "" simply means "I'm starving/I'm very hungry". So, my first interpretation of that is that it is used as interjection to strengthen the expression. Is it correct or not? But, anyway, means also "already", so I wonder if "" can means also "I'm already starving".

The meaning of in actually depends on the context.

Possible meanings:

"I'm already hungry."

"I'm really hungry."

"I'm hungry now."

etc.

Without context, this is all I could say. **In speaking, believe it or not, is pronounced differently depending on what meaning it is being used for**.