Legen kontrollerer tilstanden.

Because legen is the definite singular form of lege (doctor).

• en lege = a doctor
• legen = the doctor

In Norwegian, definiteness is usually added to the end of the noun instead of using a separate word like English the.

For the same reason: tilstanden is the definite singular form of tilstand.

• en tilstand = a condition / a state
• tilstanden = the condition / the state

So both nouns in the sentence are definite:

• Legen = the doctor
• tilstanden = the condition

Because Norwegian usually marks the by attaching it to the noun.

Compare:

• English: the doctor

• Norwegian: legen

• English: the condition
• Norwegian: tilstanden

This is very normal in Norwegian. The ending often does the job that the does in English.

It follows the standard Norwegian Subject–Verb–Object pattern:

• Legen = subject
• kontrollerer = verb
• tilstanden = object

So it works very much like English:

• The doctor checks the condition

This makes the sentence structure fairly easy for English speakers to recognize.

Kontrollerer is the present tense of the verb å kontrollere.

• å kontrollere = to check / inspect / monitor / examine, depending on context
• kontrollerer = checks / is checking / monitors

In Norwegian, the present tense is often formed with -r:

• å snakke → snakker
• å kontrollere → kontrollerer

Unlike English, the same present-tense form is used for all persons:

• jeg kontrollerer
• du kontrollerer
• han/hun kontrollerer

No extra -s like English he checks.

Not always. This is an important point.

Although å kontrollere can sometimes look like English to control, in many contexts it means:

• to check
• to inspect
• to examine
• to monitor

So in a medical sentence like Legen kontrollerer tilstanden, it often means something like:

• The doctor checks the condition
• The doctor examines the condition
• The doctor monitors the condition

So this word can be a bit of a false friend if you assume it always means control in the English sense.

No. Tilstand is a broader word meaning condition, state, or status.

It can be used for:

• a person’s health condition
• the condition of a machine
• the state of a building
• a general situation or status

In this sentence, because the subject is the doctor, English speakers will usually understand tilstanden as a medical condition.

Both are usually treated as common gender nouns, which is why they use en in the singular indefinite form:

• en lege
• en tilstand

And their definite singular forms become:

• legen
• tilstanden

For a learner, the most useful pattern here is:

• en + noun
• noun + -en for the noun

You would use the indefinite forms of the nouns:

• En lege kontrollerer en tilstand.

That means:

• A doctor checks a condition

Compare:

• Legen kontrollerer tilstanden. = The doctor checks the condition.
• En lege kontrollerer en tilstand. = A doctor checks a condition.

So the endings and articles change together depending on whether the noun is definite or indefinite.

In Norwegian, yes/no questions usually put the verb first, before the subject:

• Kontrollerer legen tilstanden?

That means:

• Is the doctor checking the condition?
• Does the doctor check the condition?

This verb-first pattern is very common in Norwegian questions.

A rough guide for an English speaker might be:

• Legen ≈ LAY-gen
• kontrollerer ≈ kon-tro-LAIR-er
• tilstanden ≈ TIL-stan-den

A few notes:

• The g in legen is pronounced.
• The r sounds are Norwegian r sounds, which may vary by dialect.
• The stress is typically on:
  • LE-gen
  • kontrol-LE-rer
  • TIL-standen

This is only an approximation, but it can help you get started.

Yes, grammatically it could. The sentence itself only says:

• The doctor checks the condition/state

Without extra context, tilstanden could theoretically refer to:

• a patient’s condition
• an injury
• a body part
• even something non-medical in a broader context

But in normal use, with the doctor as the subject, most people will naturally interpret it as a medical condition or the patient’s condition.