Svo lengi sem gólfið er kalt, geng ég í inniskónum mínum.

Svo lengi sem means as long as or so long as.

It introduces a subordinate clause and sets the condition or time span for the main clause:

• Svo lengi sem gólfið er kalt = As long as the floor is cold

It is very natural when you mean for the whole time that this remains true.

This is because of Icelandic verb-second word order.

When the sentence starts with something other than the subject — here, the subordinate clause Svo lengi sem gólfið er kalt — the finite verb of the main clause usually comes next, and the subject comes after it:

• Svo lengi sem gólfið er kalt, geng ég ...

If the sentence started directly with the subject, you would say:

• Ég geng í inniskónum mínum ...

So the inversion is not random; it is a normal Icelandic word-order rule.

Gólfið is the definite form, meaning the floor.

• gólf = a floor / floor
• gólfið = the floor

Icelandic usually adds the definite article to the end of the noun rather than using a separate word like English the.

Here, the speaker means a specific floor, so gólfið is the natural form.

Kalt agrees with gólfið.

The noun gólf is neuter singular, so the predicate adjective must also be neuter singular:

• gólfið er kalt = the floor is cold

Compare:

• masculine: stóllinn er kaldur
• feminine: hurðin er köld
• neuter: gólfið er kalt

So kalt is used because the thing being described is a neuter noun.

Because í often takes the dative when it means in in a static or descriptive sense, and with clothing Icelandic commonly uses í + dative to mean wearing something.

So:

• vera í skóm = to be wearing shoes
• ganga í inniskóm = to walk around in slippers / to wear slippers while walking

Here, inniskónum mínum is the dative form required by í in this expression.

Because slippers are normally thought of as a pair, just like in English.

So Icelandic usually uses the plural when talking about the slippers someone is wearing:

• inniskór = slippers
• í inniskónum mínum = in my slippers

A singular form can exist if you mean just one slipper, but in ordinary use the plural is the normal choice.

Because Icelandic shows grammatical information in more than one place.

The possessive mínum must agree with the noun in case, number, and gender:

• inniskónum = dative plural
• mínum = also dative plural masculine

So mínum matches the noun grammatically.

This is very normal in Icelandic. English says my slippers, but Icelandic marks the relationship more visibly through inflection.

Literally, ganga means walk or go on foot.

In this sentence, though, geng ég í inniskónum mínum is naturally understood as I walk around in my slippers or I wear my slippers while moving around.

If you only wanted to say I am wearing my slippers, with no idea of walking around, Icelandic would more likely use:

• Ég er í inniskónum mínum.

So ganga adds the sense of moving about, not just wearing.

Yes. The comma separates the initial subordinate clause from the main clause:

• Svo lengi sem gólfið er kalt, = subordinate clause
• geng ég í inniskónum mínum. = main clause

This is standard punctuation in Icelandic when a subordinate clause comes first.

Yes. You could say:

• Ég geng í inniskónum mínum svo lengi sem gólfið er kalt.

That means the same thing.

The version with Svo lengi sem ... first gives a little more emphasis to the condition as long as the floor is cold, while the version starting with Ég sounds a bit more straightforward and neutral.