I will have a speaking test in English this sunday.

⇒ I will have a speaking test in English this Sunday. 

So I practice to speak English after getting at home.

⇒ So I have to practice to speaking English after when I getting at home. 

the first qustion of the exam called 'OPIC'is introducing my self.

⇒ The first question of in the exam called 'OPIc' is entitled as introducing my self.  "Self-introduction".

I wan to talking about the reason why I'm eager to study English and asking for understanding on my ability in English not well at the answer. -

⇒ I want to talking about the reason why I'm eager to study English and asking for understanding on my ability in English which is not well. at the answer. - 

I am in charge of assisting the project manager and then our client company are in Germany.

⇒I am in charge of assisting the Project Manager and then our Client company which is in Germany. 

Somtimes, I get a situation that I have to conversate with foreigners for my company's project.

⇒Somtimes, I get in a situation that I have to converse with foreigners for my company's project. 

Most of my co-workers can speak English well. But I am not.

⇒Most of my co-workers can speak English well. But I am can't.

Since I make up my mind to study English hard, I applied for English speaking test!

⇒Since I made up my mind to study English hard, I applied for an English speaking test!

Hi Song, thank you again for this composition. I am happy that you always make time for to write something. I can see that you are reallt very eager to study English. I am sure that you will succeed if you just continue to work hard. Good job!

-Meril