I will have a one year internship in Olomouc with 500$ / month. Is it possible to live alone there with such salary ( Paying Bills of : Rental/ Electricity/ Gas/ Internet/ Food and transport ) and try to economize some money till the end of internship?
Question #1: Can you make it on $500? Short answer: It's going to be tight, but yes.
Question #2: Can you save a reasonable amount of money? Probably not.
Salary after tax
Before we start, we need to calculate the amount of tax you will pay. As of 2016, 500$ equals ~12100CZK, which after tax would be ~10400CZK. I'll be using the Czech currency from now onwards.
Renting your own flat can be done as cheap as 5000CZK, including utilities.
Living in a dorm as a non-student would be too expensive, so that's out.
Getting a room in a shared flat can be done for around 2500 CZK.
A monthly ticket for public transport costs 230 CZK.
From personal experience, you can easily cook at home for around 3000CZK per month, assuming you don't buy caviar or alcohol every day.
A basic phone plan is around 200CZK per month.
You'll probably need stuff like toothpaste, washing liquids, occasional pair of socks, etc, but that's really hard to calculate. Assume that the prices are whatever they are in your country + 20% tax.
To cover the basic expenses (and live in a personal flat) you will need: 5000+3000+230+200 = 8430CZK, which leaves ~2000CZK per month for other expenses. You could also save an extra 2500CZK by living with flatmates.
Since non-essential expenses will inevitably crop up, I'd be surprised if you've managed to save more than a few hundred bucks over the whole year. A flight from Tunisia to Prague is around 300$, so perhaps you could cover that, but not much more.