Sisälämpötila on liian korkea.

It is a Finnish compound noun:

• sisä- = inside, interior, indoor
• lämpötila = temperature

So sisälämpötila literally means indoor temperature or inside temperature.

Finnish forms compounds very freely, and they are normally written as one word. This is much more common in Finnish than in English.

On means is.

It is the 3rd person singular present tense form of the verb olla = to be.

So:

• minä olen = I am
• sinä olet = you are
• hän on = he/she is
• se on = it is

In this sentence, Sisälämpötila on... = The indoor temperature is...

Finnish has no articles, so it does not use words like a, an, or the.

That means sisälämpötila can mean:

• the indoor temperature
• an indoor temperature
• sometimes just indoor temperature

The exact meaning comes from context, not from an article.

Liian means too in the sense of more than is acceptable, desirable, or comfortable.

So:

• liian korkea = too high

This is different from very high:

• hyvin korkea = very high
• erittäin korkea = extremely/very high
• liian korkea = too high

So liian usually suggests a problem.

Yes. Korkea literally means high, and Finnish uses the same idea as English here:

• high temperature
• low temperature

So:

• lämpötila on korkea = the temperature is high
• lämpötila on matala = the temperature is low

This is completely normal Finnish usage.

Because liian is an adverb modifying the adjective korkea.

In Finnish, adverbs like liian usually come before the adjective they modify:

• liian korkea = too high
• erittäin kylmä = extremely cold
• melko hyvä = fairly good

So liian korkea is the natural order.

Here korkea is a predicate adjective after the verb olla (to be).

The structure is:

• Sisälämpötila = subject
• on = verb
• liian korkea = predicate

In this kind of simple sentence, the adjective is in its basic dictionary form, which is the nominative singular: korkea.

So this sentence is not using korkea as an object or in some other case. It is simply describing the subject.

It is in the nominative case, which is the basic form and the usual case for the subject of a sentence.

Here:

• Sisälämpötila = the subject
• on = is
• liian korkea = too high

So sisälämpötila is just the thing being talked about.

The given sentence has the most neutral word order:

• Sisälämpötila on liian korkea.

Finnish word order is more flexible than English word order, but changing it usually changes the focus or emphasis.

For example:

• Sisälämpötila on liian korkea. = neutral statement
• Liian korkea sisälämpötila... = this becomes a noun phrase, meaning an indoor temperature that is too high, not a complete sentence by itself

So for a normal, straightforward sentence, the original order is the best one to learn first.

These are important Finnish vowels:

• ä as in sisä-
• ö as in lämpötila

Approximate help for English speakers:

• ä is somewhat like the vowel in cat, but usually cleaner and more consistent
• ö has no exact English equivalent; it is similar to German ö or Swedish ö

A few useful pronunciation notes:

• Finnish stress is usually on the first syllable
• each written vowel is pronounced clearly
• spelling and pronunciation match quite closely in Finnish

So roughly:

• sisä → SI-sä
• lämpötila → LÄM-pö-ti-la
• korkea → KOR-ke-a

In korkea, the ending -ea is pronounced as two vowel sounds, not one merged sound.