Mobilsignalet er værre i dag.

Because Danish very often makes compound nouns where English uses two or more words.

• mobil = mobile phone / cell phone
• signal = signal
• mobilsignal = mobile signal, cell signal
• mobilsignalet = the mobile signal

So Danish prefers one combined noun instead of something like mobil signal.

The ending -et is the definite article attached to the noun. In English, you usually put the before the noun, but in Danish it is often added to the end.

• et mobilsignal = a mobile signal
• mobilsignalet = the mobile signal

Here, signal is a common neuter noun, so its definite singular ending is -et.

In Danish, the definite article is usually a suffix, not a separate word.

So:

• English: the mobile signal
• Danish: mobilsignalet

A separate definite word like det is only used in certain cases, for example with an adjective:

• det dårlige mobilsignal = the bad mobile signal

But in your sentence, there is no adjective before the noun, so mobilsignalet by itself is enough.

Er is the present tense of at være = to be.

So:

• jeg er = I am
• du er = you are
• det er = it is
• mobilsignalet er = the mobile signal is

In this sentence, er links the subject mobilsignalet with the description værre i dag.

Værre is the comparative form of slem or, in many real-life cases, also used where English would say worse.

Danish often uses værre in everyday speech for things like signal, weather, pain, noise, conditions, and so on.

So:

• dårlig = bad
• dårligere = worse / more bad
• værre = worse

In many contexts, both may be possible, but værre is very natural here.
So Mobilsignalet er værre i dag means The mobile signal is worse today.

Because Danish, like English, can leave the comparison understood.

Værre is a comparative form, so the full idea is something like:

• worse than before
• worse than usual
• worse than yesterday

But if the context already makes that clear, Danish does not need to say it explicitly.

If you wanted to include it, you could say something like:

• Mobilsignalet er værre end i går. = The mobile signal is worse than yesterday.

I dag means today.

Literally:

• i = in
• dag = day

But together, i dag functions like the adverb today.

It is normally written as two words in modern Danish:

• i dag

Example:

• Jeg arbejder hjemme i dag. = I’m working from home today.

In normal usage, mobilsignalet usually refers to mobile reception / cell signal rather than some technical signal in an abstract sense.

So a natural English understanding is:

• The cell reception is worse today.
• The mobile signal is worse today.

Both are good translations depending on context.

The word order is very straightforward:

• Mobilsignalet = subject
• er = verb
• værre = complement
• i dag = time expression

So the pattern is:

Subject + verb + description + time

That is very similar to English: The mobile signal + is + worse + today

Yes. That is also correct.

Danish follows the V2 rule, which means the finite verb usually comes in the second position of a main clause.

So both are correct:

• Mobilsignalet er værre i dag.
• I dag er mobilsignalet værre.

The second version puts more focus on today.

A rough guide is something like VAIR-uh, but with Danish sounds that do not match English exactly.

A few useful points:

• æ is a front vowel, somewhat like the vowel in English air for many speakers, but not exactly.
• The double rr does not mean you strongly roll the r.
• The final -e is usually a light, weak vowel.

So do not try to pronounce it like a fully clear English verry. The Danish sound is softer and more central.

No. Signal is a neuter noun, so it takes et.

• et signal
• et mobilsignal
• mobilsignalet

That means forms like en mobilsignal would be incorrect.

Yes, absolutely. It is short, natural, and idiomatic.

A Danish speaker could easily say this in everyday situations like:

• poor reception at home
• bad signal on the train
• weak network in a rural area

It sounds like normal spoken or written Danish.