De vill öka bufferten.

De is the subject pronoun here, and it corresponds to they in English.

In De vill öka bufferten, de is the one doing the action:

• De = they
• vill = want
• öka = increase
• bufferten = the buffer / the reserve

A useful extra note: in everyday spoken Swedish, de is usually pronounced like dom.

Because vill is a modal verb, and in Swedish, modal verbs are followed directly by the infinitive without att.

So:

• De vill öka bufferten = correct
• De vill att öka bufferten = incorrect

This works like:

• kan göra = can do
• ska gå = will / shall go
• måste läsa = must read
• vill öka = want to increase

Even though English uses to after want, Swedish does not use att after vill in this structure.

Öka is in the infinitive form, because it comes after the modal verb vill.

Compare:

• De vill öka bufferten. = They want to increase the buffer.
• De ökar bufferten. = They are increasing / increase the buffer.

So:

• vill = finite verb, present tense
• öka = infinitive

This is a very common Swedish pattern:

• Jag vill läsa.
• Hon kan komma.
• Vi måste gå.

The ending -en makes the noun definite singular, meaning the buffer rather than just a buffer.

So:

• en buffert = a buffer
• bufferten = the buffer

This is a key feature of Swedish: the definite article is usually attached to the end of the noun.

Other examples:

• en bil = a car

• bilen = the car

• en plan = a plan
• planen = the plan

So bufferten is not a different word; it is just the definite form of buffert.

It is an en word:

• en buffert
• bufferten

That is why the definite form ends in -en.

If it were an ett word, the definite ending would normally be -et instead.

The word order is:

Subject + finite verb + infinitive + object

So here:

• De = subject
• vill = finite verb
• öka = infinitive
• bufferten = object

This is a normal Swedish main-clause pattern, and it looks quite similar to English in this sentence.

Also remember that Swedish main clauses usually follow the V2 rule: the finite verb comes in the second position.

Since the subject comes first here, the sentence looks straightforward:

• De | vill | öka bufferten

Because de is the subject form, while dem is the object form.

Here, they are doing the wanting, so Swedish uses de.

Compare:

• De vill öka bufferten. = They want to increase the buffer.
• Jag ser dem. = I see them.

In speech, both de and dem are often pronounced dom, which is why learners sometimes find the spelling confusing.

You add inte after the finite verb:

• De vill inte öka bufferten. = They do not want to increase the buffer.

This is a very common Swedish pattern:

• subject
• finite verb
• inte
• infinitive / rest of sentence

Examples:

• Jag kan inte komma.
• Hon ska inte jobba.
• Vi vill inte vänta.

So in your sentence:

• De vill inte öka bufferten.

Yes. Öka can be used both intransitively and transitively.

Intransitive:

• Priserna ökar. = Prices are increasing.

Transitive:

• De ökar bufferten. = They increase the buffer.
• De vill öka bufferten. = They want to increase the buffer.

So in your sentence, öka is being used transitively, because it has a direct object: bufferten.

In everyday spoken Swedish, de is usually pronounced dom.

So although the sentence is written:

• De vill öka bufferten

it will often sound more like:

• Dom vill öka bufferten

This is very common in spoken Swedish. Traditional standard writing usually keeps de for the subject form and dem for the object form, but learners should know that the spoken pronunciation is often the same.

The sentence as written is in the present tense because of vill.

Present:

• De vill öka bufferten. = They want to increase the buffer.

Past:

• De ville öka bufferten. = They wanted to increase the buffer.

The infinitive öka stays the same after the modal-like verb:

• vill öka
• ville öka

So the tense change happens in vill → ville, not in öka.