你好。我是老師

我住在台灣. 我教英語，在明明鏡高中教英文。我想學習中文國。但是，中文國是非常困難學的。

When you start learning a language, it is best to provide an English version as well.  This way it removes much guesswork out and at the same time to show you the precise nuance you are trying to convey.

As in English, "Chinese" may refer to the language, the culture, its traditions etc but never to its country.  中國 = China, 中文 = the Chinese language, 中式 = Chinese style.  The trickier one is "The Chinese People".  Depending on where you are, it is used very differently because of political situations.  Overseas Chinese or those not born in China or Taiwan would use 華人.  For Koreans, Japanese, may use 漢人 and Cantonese use 唐人 (since Canton was incorporated into the Chinese Empire during the Tang Dynasty).

It took me a while to figure out that 明明鏡高中 is an error.  You are referring to a highschool named Bright Mirror.  It mislead me to think of 明鏡高懸

你好,我是老師。

我住在台灣。 我在明明鏡高中教英語。我想學習中文。但是，中文是非常困難的。

你好。我是老師

我住在台灣. 在明鏡高中教英语。我想學習中文。但是，中文对我来说是非常困難的。

你好。我是老師

我住在台灣. 我教英語，在明明鏡高中。我想學習中文國。但是，中文國是非常困難的。