Learn Hardcore Finnish: Tyttö on taitava kielissä. - The girl is skilled at languages.

Finnish expresses “good/skillful at X” with the inessive, literally “in X.” With adjectives like taitava, hyvä, huono, heikko, vahva, lahjakas, you typically use the inessive:

taitava kielissä = skillful in languages (i.e., good at languages)
hyvä matematiikassa = good at math
huono kieliopissa = bad at grammar

Why is kielissä plural? Could I use the singular?

It’s plural because you’re talking about the domain of languages in general. Singular kielessä would mean “in the language,” which sounds like one specific language. For a specific language, you don’t say kielessä; you name the language:

hyvä suomessa/ruotsissa/englannissa = good at Finnish/Swedish/English (as a subject/skill)

How is kielissä formed?

Breakdown: kieli (language) + plural marker -i- + inessive -ssa/-ssä → kieli + i + ssä → kielissä.
Because the stem has only neutral vowels (e, i), vowel harmony selects the front variant -ssä.

Why is taitava in the nominative and not affected by kielissä?

Taitava is a predicative adjective describing the subject tyttö after the verb on (is). Predicative adjectives agree with the subject’s case and number, not with adverbials. Here the subject is nominative singular, so taitava is nominative singular.

Can I change the word order? For example, put kielissä somewhere else?

Yes. Finnish word order is flexible and used for emphasis/information structure:

Neutral: Tyttö on taitava kielissä.
Focus on the domain: Tyttö on kielissä taitava.
Contrastive/topic-first: Kielissä tyttö on taitava (mutta matematiikassa ei).

How would this sentence look with a plural subject?

Default: Tytöt ovat taitavia kielissä. (partitive plural predicative is common)
More “set-like”/categorical: Tytöt ovat taitavat kielissä.
Both are possible; the first is the everyday default, the second can emphasize a defined group with a property.

Is there a difference between taitava and hyvä here?

taitava = skilled, proficient, talented (often suggests developed skill)
hyvä = good (broader, more general)
Both work: Tyttö on taitava/ hyvä kielissä. Taitava can sound a bit stronger or more skill-focused.

What’s the difference between kielissä, kielillä, and kieliä?

kielissä (inessive plural) = in languages (the domain; used after adjectives like taitava, hyvä)
kielillä (adessive plural) = on/with languages; not used here. Note: puhua kielillä means “to speak in tongues” in a religious sense.
kieliä (partitive plural) = some languages/any languages as objects: Hän osaa useita kieliä = He/She knows several languages.

Could I say something like “She knows/ speaks several languages” instead?

Yes, as a different phrasing:

Hän osaa useita kieliä. = She knows several languages.
Hän puhuu monta kieltä. = She speaks many languages.
These talk about actual languages known/spoken, while taitava kielissä is about general aptitude.

Are there other natural ways to express the same idea?

Hän on hyvä kielissä.
Hän on lahjakas kielissä.
Hän on kielitaitoinen.
Hänellä on hyvä kielitaito.

Does Finnish need an article here (“a/the girl”)?

No. Finnish has no articles. Tyttö can mean either “a girl” or “the girl,” depending on context. If you need specificity, you use context, pronouns, or other determiners.

How do I pronounce the tricky parts?

tyttö: y and ö are front rounded vowels (like French u and eu). Double tt means a long consonant.
taitava: the diphthong ai as in “eye.”
kielissä: two syllables at the start kie-li-, then long ss in -ssä. Stress the first syllable of the word.

Could I use taitavasti instead of taitava?

No in this structure. Taitava is an adjective complement after on. Taitavasti is an adverb and modifies verbs: Hän puhuu taitavasti = “She speaks skillfully.”

What happens in the negative?

Negate the verb: Tyttö ei ole taitava kielissä. The adverbial kielissä stays the same, and the predicative taitava commonly remains nominative singular in this kind of sentence.

Is dropping on possible, like in some colloquial Finnish?

In standard Finnish, you keep on: Tyttö on taitava… In casual speech, some people might omit on in certain contexts, but that’s colloquial and not recommended for learners.