Đây là vấn đề chung.

Here, đây works like this in English, and in the pattern đây là ..., it often corresponds to this is ....

So:

• đây = this / here
• đây là = this is

In this sentence, đây is pointing to the thing being talked about.

This is a very common learner question.

• đây can stand on its own as this / here
• này usually comes after a noun to mean this

Compare:

• Đây là vấn đề chung. = This is a common/general issue.
• Vấn đề này là vấn đề chung. = This issue is a common/general issue.

So đây is natural because it can be the thing at the start of the sentence.
You would not normally use này by itself in the same way.

Là is the linking word, similar to to be in English in sentences like X is Y.

Structure:

• Đây = this
• là = is
• vấn đề chung = a common/general issue

So the pattern is:

Đây + là + noun phrase

A useful note: Vietnamese often does not use là before simple adjectives. For example:

• Trời đẹp. = The weather is beautiful.

But when identifying or classifying something as a noun phrase, là is very common and natural:

• Đây là giáo viên. = This is a teacher.
• Đây là vấn đề chung. = This is a common/general issue.

Because in Vietnamese, adjectives usually come after the noun they describe.

So:

• vấn đề = issue / problem
• chung = common / shared / general

Together:

• vấn đề chung = common issue or general issue

This noun + adjective order is very normal in Vietnamese.

Compare:

• nhà đẹp = beautiful house
• người tốt = good person
• vấn đề chung = common/general issue

In meaning, it is best treated as one vocabulary item: vấn đề = issue / problem / matter.

Vietnamese writing puts spaces between syllables, so many single lexical items appear as two written parts. That can be confusing for English speakers.

So although it is written as:

• vấn đề

you should learn it as one unit of meaning.

Vietnamese often leaves nouns bare when English would use a or the.

So Đây là vấn đề chung is perfectly natural.

If you add một:

• Đây là một vấn đề chung.

that is also grammatical, but it can sound a bit more like This is a common issue / one common issue as a specific example.

Without một, the sentence can feel a little more general or classifying. Vietnamese does this much more freely than English.

Chung has a few related meanings, and the exact nuance depends on context. Here it can suggest:

• common
• general
• shared

So vấn đề chung can mean something like:

• an issue many people have
• a general issue, not a private or isolated one
• a shared problem

Depending on context, another Vietnamese word you may also see is phổ biến, which often means common in the sense of widespread.

For example:

• vấn đề chung = a shared/general issue
• vấn đề phổ biến = a widespread/common issue

A simple breakdown:

• đây — roughly like day, but with a Vietnamese đ
• là — low falling tone
• vấn — rising tone
• đề — low falling tone
• chung — level tone

A rough pronunciation guide for an English speaker:

• đây là vấn đề chung
  ≈ day laa vun de chung

A few important notes:

• đ is not English d exactly; it is a stronger Vietnamese d sound
• â in đây is not a plain English vowel, so the day comparison is only approximate
• tones matter, especially in là, vấn, and đề

If you want to sound natural, it is better to learn the sentence by listening and repeating rather than relying only on English-style spelling.

Yes. Vietnamese does not mark articles the way English does, so the English translation depends on context.

Vấn đề chung could be understood as:

• a common issue
• the common issue
• a shared issue
• the general issue

English forces you to choose more than Vietnamese does. Vietnamese often leaves that flexible and lets context do the work.

It is grammatical and natural, but the best wording depends on what exactly you want to emphasize.

Some related options are:

• Đây là vấn đề chung.
  This is a general/shared issue.

• Đây là vấn đề phổ biến.
  This is a common/widespread issue.

• Đây là vấn đề chung của nhiều người.
  This is an issue many people share.

So the original sentence is fine, but in real conversation Vietnamese speakers might choose a slightly different version depending on whether they mean general, shared, or widespread.