Því meira sem við æfum okkur, því betur skiljum við íslenskuna.

It is the Icelandic way to express the correlative pattern the more ..., the more/better ....

So:

• Því meira sem við æfum okkur = the more we practice
• því betur skiljum við íslenskuna = the better we understand Icelandic

This structure is extremely common in Icelandic. You can think of því here as part of a fixed comparison pattern rather than giving it a simple one-word translation.

Because meira is being used adverbially here.

The sentence is not really saying the bigger practice or the greater practice. It means the more we practice, where more modifies the action practice.

A useful comparison:

• meiri = comparative form used more like an adjective, agreeing with a noun
• meira = neuter form, often used adverbially, especially in patterns like the more ...

So in Því meira sem við æfum okkur, meira means more in the sense of to a greater extent.

In this structure, sem links the comparative phrase to the clause that follows it.

So:

• Því meira sem við æfum okkur = literally something like by-that more that we practice

But in natural English, it just becomes the more we practice.

You do not usually translate sem separately in this kind of sentence. It is just part of the standard Icelandic pattern.

Okkur means ourselves/us, and here it is part of the verb phrase æfa sig, which often means to practice or to train oneself.

So:

• við æfum okkur = we practice
• more literally: we practice ourselves

This is a very common reflexive construction in Icelandic. English usually does not say we practice ourselves in this context, but Icelandic often uses the reflexive pronoun where English would not.

Not always.

The verb æfa can also take a direct object:

• að æfa lag = to practice a song
• að æfa íslensku = to practice Icelandic

But æfa sig is also very common, especially when the meaning is to practice/train oneself in general.

So these can both work, depending on nuance:

• við æfum okkur = we practice / we train ourselves
• við æfum íslensku = we practice Icelandic

In your sentence, æfum okkur sounds very natural.

Because betur is the comparative adverb of vel (well).

Compare:

• vel = well
• betur = better
• best = best

Since it describes how well we understand, Icelandic uses the adverb:

• við skiljum betur = we understand better

By contrast, betra is a form of the adjective betri (better) and would be used differently, for example with nouns or in predicate adjective structures.

So here betur is exactly the right form.

This is because Icelandic is a verb-second language.

In main clauses, the finite verb often comes in the second position. Here, the sentence begins with the adverbial comparative phrase:

• því betur

Since that first element takes the first slot, the verb comes next:

• því betur skiljum við íslenskuna

So the order is:

1. því betur
2. skiljum
3. við
4. íslenskuna

If you are an English speaker, this may feel inverted, but it is normal Icelandic syntax.

Because íslenskuna is the definite form: the Icelandic language.

Compare:

• íslenska = Icelandic
• íslenskan = the Icelandic language
• íslenskuna = the Icelandic language in the accusative case

In this sentence, the speaker is talking about Icelandic as a specific language being understood, so the definite form is natural.

English often says simply Icelandic, but Icelandic frequently uses the definite form in cases like this.

It is in the accusative singular definite.

That is because skilja (to understand) normally takes a direct object in the accusative:

• að skilja íslensku = to understand Icelandic
• að skilja íslenskuna = to understand the Icelandic language

So íslenskuna is the object of skiljum, and that is why it appears in the accusative form.

Not very naturally.

A rough literal breakdown is:

• Því meira = by-that more
• sem við æfum okkur = that we practice ourselves
• því betur = by-that better
• skiljum við íslenskuna = understand we the-Icelandic-language

But the natural English meaning is simply:

The more we practice, the better we understand Icelandic.

So this is a sentence where understanding the structure is more useful than trying to translate each word mechanically.

The letter þ is pronounced like the th in thing, not like the th in this.

So:

• Því begins with the unvoiced th sound /θ/

This letter is called thorn. It is very common in Icelandic, and English speakers usually need a little practice with it at first.

Yes, that would also be a good Icelandic sentence.

It means something like:

The more we practice Icelandic, the better we understand it.

The difference is mainly one of wording:

• við æfum okkur = we practice / train ourselves
• við æfum íslensku = we practice Icelandic specifically

Your original sentence is perfectly natural, but this alternative is also very plausible if you want to name the thing being practiced directly.

The big takeaway is this pattern:

Því + comparative + sem-clause, því + comparative + main clause

Examples:

• Því meira sem þú lest, því betur talarðu.

  • The more you read, the better you speak.

• Því fyrr sem við förum, því betra.

  • The sooner we go, the better.

So your sentence is a very useful model for building similar comparisons in Icelandic.