Why did I start to study English althoughwhen there are a lot of other foreign language.s?

Questions have a question mark, "?", at the end. Also, the plural of "language" is "languages".

You could also say, "Why did I choose to study English when there are so many other foreign languages?"

Edited slightly for clarity. The original sentence made sense, but this is clearer.

The reason why I selected English is because I want to be a world-wide person of my work.

I understand what you mean. "world-wide" makes sense to me, but it may not to others. I don't know any synonyms, sadly.

If you say, "The reason I selected English", the "why" in that sentence is implied. When you say "The reason", you are about to explain why, so it's not necessary to say it here.

(I hope that makes sense)

I work as a public officer of the Japanese government who specializes in a national security.

Pretty good! Just a small edit.

When I was a university student, I was worried about our rapidly changing our world rapidly.

Just moved a few words around to make it more clear. You could also say, "I was worried about our world changing rapidly."

I want to protect my country and people from the negative impact caused by the change.

Small correction. "The negative impact was caused by the change."

Unless you meant, "the negative impact causing the change." - that would also work, but it means something different.

So, I thought I should learn foreign language skills to be committed to them.

"earn" makes sense, but "learn" is probably better here.

I'm not entirely sure what you mean by "to be committed them", but if that is what you mean, you would have a "to" in there. You are committed to something.

English is a publiccommon language in the worldmany places.

From what I can tell, you are referring to how it is widely-spoken and considered "default" or "common" in a lot of countries.

(When I say default, I refer to countries like America and The United Kingdom, places like that. It is spoken outside of those spaces, too.)

Therefore, as a first step to becoming a world-wide person, I started to learn English!

Small correction. You could say either "being" or "becoming", either works.

I’m a beginner of learning English.

No need for the of

Why did I start to study English although there are a lot of foreign languages.

No need to add this context, it can be combined with the following sentence, plural languages

The reason why I selectedchose English is to be a world-wide person of my work.

chose is more common to use

I work as a public officer ofor the Japanese government who, specializeing in a national security.

No need to include the who, you can use specializing here because the context is still on you, also you can remove the 'a'. Also changed of to for the

When I was a university student, I was worried about our rapidly changing our world rapidly.

The original is putting it in the context about you chaing the world rapidly but I think what you meant to say was the world changing rapidly.

I want to protect my country and people from the negative impacts caused by theis change.

caused

you also just say change but I added this to refer back to the change mentioned in the prior sentece

So, I thought I should earndevelop foreign language skills to be committed to them.

earn is more like you gained something, in this context you're learning/developing

committed to them

English is a publicwidely used language in the world.

I'm more familiar with the widely used than public as an english speaker

Therefore, as amy first step to becoming a world-wide person, I started was to learn English!

the context of this sentence is speaking towards that of the past of what you first step was so I changed that last part