Jo flere langrennsski vi smører, desto nyttigere er smøreprofilen.

It is the Norwegian correlative comparative pattern, equivalent to English the more ..., the more ... or the X-er ..., the Y-er ....

So:

• Jo flere langrennsski vi smører = The more cross-country skis we wax
• desto nyttigere er smøreprofilen = the more useful the wax profile is

This pattern shows that one thing changes together with another.

Yes. In modern Norwegian, jo ... jo ... is very common:

• Jo flere langrennsski vi smører, jo nyttigere er smøreprofilen.

That means the same thing.
Jo ... desto ... is also fully correct, but can sound a bit more formal or written.

Because langrennsski is a countable plural noun.

Use:

• flere for countable things = more / a greater number of
• mer for uncountable things or amounts = more

So:

• flere langrennsski = more cross-country skis
• but mer snø = more snow

Because Norwegian forms compound nouns much more readily than English does.

So English often uses several words where Norwegian uses one:

• langrenn
  • ski → langrennsski
• smøre
  • profil → smøreprofil

This is very normal in Norwegian. If you split these up, it often looks unnatural or wrong.

Because ski often has the same form in singular and plural in Norwegian, especially in compounds.

So you can have:

• en ski
• flere ski

And in compounds:

• en langrennsski
• flere langrennsski

The word flere already makes the plural meaning clear, so no extra plural ending is needed here.

Because the clause introduced by jo behaves like a subordinate clause.

In Norwegian subordinate clauses, the subject normally comes before the finite verb:

• ... vi smører

If it were an ordinary main-clause word order after a fronted element, you would expect inversion:

• ... smører vi

But that is not what happens here. In the jo ... desto ... pattern, the first clause typically keeps subordinate-clause word order.

Because Norwegian main clauses follow the V2 rule: the finite verb normally comes in the second position.

Here, desto nyttigere is placed first in the clause. Once that happens, the finite verb must come next:

• desto nyttigere er smøreprofilen

So the order is:

1. fronted element: desto nyttigere
2. finite verb: er
3. subject: smøreprofilen

This inversion is completely normal in Norwegian main clauses.

Nyttigere is the comparative form of nyttig.

• nyttig = useful
• nyttigere = more useful
• nyttigst = most useful

So desto nyttigere means the more useful.

For learners, the important point is that Norwegian often makes comparatives with -ere, where English uses more.

Smøreprofilen is:

• the compound noun smøreprofil
• plus the definite ending -en

So:

• en smøreprofil = a wax profile / waxing profile
• smøreprofilen = the wax profile / the waxing profile

Norwegian usually marks definiteness by adding an ending to the noun, instead of using a separate word like English the.

Because the sentence expresses a general relationship or general truth, not one specific event.

Norwegian often uses the present tense for statements like this, just as English does:

• The more we practice, the better we get.
• Jo mer vi øver, desto bedre blir vi.

So smører and er are present tense because the sentence describes a general rule or tendency.

In this skiing context, yes, that is the natural translation.

The basic verb å smøre has a broad meaning such as to spread, to grease, to lubricate, or to apply something. But with skis, it commonly means to wax them.

So the exact English translation depends on context, but in this sentence wax is the idiomatic choice.

Yes. The first part is still a full clause:

• Jo flere langrennsski vi smører

The phrase flere langrennsski is the object, and vi smører provides the subject and verb. So even though the clause begins with the comparative phrase, it is still structurally complete.

This is common in the jo ... desto ... pattern: the quantity or degree being compared is placed early in the clause.