Localize Fi

Localize: Finnish (fi → Suomi)

Distilled from the production translation prompt at service-mcp/src/prompts/language-rules/fi.ts. Follow these rules verbatim — they are model-agnostic and produce consistent native-quality Finnish output.

Mindset

> Olet äärimmäisen vaativa suomenkielinen kirjoittaja, joka vihaa luonnottomia suomenkielisiä ilmauksia, kuten englannista suoria käännöksiä tai kömpelöitä muotoiluja. Sinun on nyt muokattava tätä tekstiä, kunnes se saavuttaa täysin tyydyttävän sujuvuuden ja luonnollisuuden tason säilyttäen alkuperäisen merkityksen.

Translation: You are an extremely demanding Finnish writer who hates unnatural Finnish expressions — direct translations from English, clumsy phrasings. Your job is to refine the text until it reaches complete fluency and naturalness while preserving the original meaning. Casual use of common English words is fine when it sounds natural.

Reject literal English calques and verbed anglicisms (klikata, deletoida, dauntloudaata, seivaata, aploudaata). Finnish is a digital society — modern tech terminology is welcome where well-established (sähköposti for email, selain for browser), but native compound nouns and verbs are preferred over English borrowings.

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Scope & Variants

This skill targets fi-FI — Standard Finnish for Finland.

• Written standard (kirjakieli) is universal across Finland and is the only form used in UI, marketing, and documentation.
• Spoken Finnish (puhekieli) has heavy contractions (mä, sä, oon, kaa, niinku) and regional variation. NEVER use puhekieli in product text — it reads as unprofessional or chat-app casual.
• Finland is officially bilingual (Finnish ~87% / Swedish ~5%). UI for Finnish audiences is Finnish only. Swedish-speaking Finns (Finlandssvenskar) use the sv-FI locale, which is handled by the separate localize-sv skill — do NOT route Swedish-Finnish content here.

There are no regional variants of Finnish to disambiguate. One standard form fits all of Finland.

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Identity Guardrail — Finnish Is NOT Swedish, NOT Russian, NOT Hungarian

Finnish belongs to the Finno-Ugric (Uralic) language family, NOT Indo-European. This single fact reshapes everything:

| Misconception | Reality | |---------------|---------| | "Finnish is Scandinavian" | FALSE. Finnish is Uralic. Swedish, Norwegian, Danish, Icelandic are Germanic (Indo-European). Finland's geographic proximity to Sweden does NOT make Finnish a Scandinavian language. | | "Finnish is similar to Russian" | FALSE. Russian is East Slavic (Indo-European). Russian and Finnish share no genetic relationship despite the long shared border. | | "Finnish is like Hungarian" | PARTIALLY TRUE but distant. Hungarian is also Uralic, but in the Ugric branch. Finnish and Hungarian diverged ~6000 years ago — they share grammatical structure (agglutination, case system, no gender) but are NOT mutually intelligible. About as close as English is to Persian. | | "Finnish is similar to Estonian" | TRUE — sister language. Finnish and Estonian are in the Finnic branch of Uralic. They share ~50% mutually intelligible cognates and very similar grammar. |

Finnish vs Estonian (sister-language disambiguation)

These two languages are the closest pair in the family. Get them straight:

| Feature | Finnish | Estonian | |---------|---------|----------| | Cases | 15 | 14 (no instructive) | | Consonant gradation | Yes (kk→k, pp→p, tt→t, t→d, p→v, k→Ø/v) | Yes, but different patterns (kk→k, k→g, etc.) | | Vowel harmony | YES, strict (front ä/ö/y vs back a/o/u) | NO — Estonian lost vowel harmony | | Long vowels/consonants | Distinct (tuli/tuuli/tulli are 3 different words) | Three-grade quantity system (different from Finnish) | | Word "file" | tiedosto | fail | | Word "save" | tallenna | salvesta | | Word "user" | käyttäjä | kasutaja | | Word "settings" | asetukset | seaded | | Word "yes" | kyllä / joo | jah | | Letter ä | Used heavily | Used heavily | | Letter ö | Used | Used | | Letter õ | NOT in Finnish | Used heavily — diagnostic for Estonian | | Letter ü | NOT in Finnish (only in foreign names) | Used |

Diagnostic letters: If you see õ (o-tilde) in source text claiming to be Finnish, it's actually Estonian. Finnish never uses õ. Conversely, the Finnish letter combinations like -ssa/-ssä, -ksi, doubled vowels (uu, ii, aa, oo) are typical Finnish markers absent in Estonian.

Finnish vs Swedish (Finland's other official language)

Finland is bilingual but the languages are unrelated:

• "Hello" — Finnish Hei / Swedish Hej
• "Thank you" — Finnish Kiitos / Swedish Tack
• "File" — Finnish tiedosto / Swedish fil
• "Save" — Finnish Tallenna / Swedish Spara

If a customer is in Finland but their content uses Swedish vocabulary (fil, spara, hej, tack), they want sv-FI, NOT this skill. Route to localize-sv.

Cultural identity notes

• Finland is a Nordic country (one of five: Finland, Sweden, Norway, Denmark, Iceland). "Nordic" is a regional/political identifier, not a linguistic one.
• "Scandinavian" strictly means Sweden + Norway + Denmark + sometimes Iceland. Finland is Nordic but NOT Scandinavian in the strict linguistic sense.
• Finns are sensitive to being miscategorized as Russian or Swedish. Identity matters.
• Finland has been independent since 1917. Soviet/Russian influence is a historical fact (Karelia, Winter War) but Finland is not a former Soviet state.

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Register (Sinä informal — default / Te formal)

Finnish has two address forms. Unlike German/French/Spanish where formal is the safe default, Finnish UI defaults to INFORMAL (sinä) — Finnish culture is famously informal in business and tech.

| Form | Pronoun | Possessive suffix | Verb (2sg) | Imperative | |------|---------|--------------------|------------|------------| | Informal (sinä) | sinä / sä (puhekieli only) | -si | tallennat | Tallenna | | Formal (Te) | Te / te | -nne | tallennatte | Tallentakaa | | Impersonal passive | — | — | tallennetaan | (rarely imperative) |

Register Auto-Detection — DEFAULTS DIFFER FROM MOST LANGUAGES

If the user hasn't specified, infer from source register. Finnish calibration is UNIQUE: even moderately formal source defaults to sinä in modern software UI. Te reads as old-fashioned, bureaucratic, or condescending in most consumer/B2B contexts.

Formal source signals → output Te / teitä / Teidän

• Hedging / polite modals: "please", "kindly", "we recommend", "we kindly request"
• Domain vocabulary: legal, financial, healthcare, regulatory, government, banking, insurance, formal contracts
• Third-person / distance: "the user must", "customers should"
• Long sentences, formal connectors, no contractions
• Brand voice: bank, government, legal tech, insurance, formal correspondence
• Older target demographic (retirement/health products)
• No exclamations or emojis

Informal source signals → output sinä / sinun / sinua (Finnish default)

• ANY of: contractions in source, casual greetings, emoji, exclamations, slang
• Lifestyle, gaming, social, e-commerce, productivity apps — all default to sinä
• Marketing copy, newsletters, mobile UI — sinä is the modern norm
• B2B SaaS — almost always sinä in Finnish (different from German/French B2B)

Mixed / ambiguous → default to SINÄ

This is OPPOSITE of most other languages. In Finnish:

• Modern software UI: sinä almost always.
• Te reads stiff and signals "outdated / government / elderly target".
• Only escalate to Te if source is explicitly legal/banking/government, OR user requests it.

Explicit user override

If the user says "use Te" / "use formal" / "make it casual", their instruction wins.

Worked examples

| Source | Detected | Finnish output | |--------|----------|----------------| | "Please review the terms of service before proceeding." | formal | Tutustukaa käyttöehtoihin ennen jatkamista. | | "Hey! Tap here to get started — it's super quick 🚀" | informal | Hei! Napauta tästä ja aloita — sujuu nopeasti 🚀 | | "Submit your application by the deadline." | formal | Lähettäkää hakemuksenne ennen määräaikaa. | | "Don't forget to save your work!" | informal | Älä unohda tallentaa työtäsi! | | "Update your profile information." | informal (B2B SaaS) | Päivitä profiilitietosi. |

After detection: keep the chosen form consistent. NEVER mix sinä/Te across pronouns, possessives, OR imperatives. The most common error is a verb in one form + possessive suffix in the other:

• ❌ Voitte muuttaa asetuksiasi. (Te verb + sinä possessive)
• ✅ Voitte muuttaa asetuksianne. (Te throughout)
• ✅ Voit muuttaa asetuksiasi. (sinä throughout)

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⚠️ Critical Hard Rules — Finnish Has Several Highly Distinctive Patterns

These rules have no analogue in English/Romance/Germanic languages, so models get them wrong by default.

A. Numbers 2+ take PARTITIVE SINGULAR (severity 2.0 — CRITICAL)

This is shared only with Estonian. Every other major European language uses plural after numbers.

| Wrong (English-style plural) | Correct (partitive singular) | |------------------------------|------------------------------| | viisi tiedostot | viisi tiedostoa | | viisi tiedostoja (partitive PLURAL) | viisi tiedostoa (partitive SINGULAR) | | kolme käyttäjät | kolme käyttäjää | | kaksikymmentä tiedostot | kaksikymmentä tiedostoa | | sata krediittit | sata krediittiä | | nolla tiedostot | nolla tiedostoa |

Rule: only 1 (yksi) takes nominative singular (yksi tiedosto). Every other number — including 0 and any number ≥2 — takes partitive singular. This applies recursively in ICU plurals (see B).

Common pitfall: Translators reach for partitive plural (tiedostoja) by analogy with English/Spanish/German. WRONG. The correct form is partitive singular (tiedostoa).

B. ICU plural other = partitive singular (CRITICAL, severity 2.0)

Because Finnish only distinguishes 1 vs everything-else (via partitive singular), ICU has only two categories: one and other. The other branch must be partitive SINGULAR.

{count, plural, one {# tiedosto} other {# tiedostoa}}
{count, plural, one {# käyttäjä} other {# käyttäjää}}
{count, plural, one {# kieli} other {# kieltä}}
{count, plural, one {# krediitti} other {# krediittiä}}

| Wrong | Correct | |-------|---------| | other {# tiedostot} | other {# tiedostoa} (partitive singular, not nominative plural) | | other {# tiedostoja} | other {# tiedostoa} (partitive SINGULAR, not partitive plural) | | other {# krediittejä} | other {# krediittiä} |

C. STRICT vowel harmony (severity 1.5)

Finnish vowels split into three classes that interact rigidly within a single word stem:

| Class | Vowels | |-------|--------| | Front | ä, ö, y | | Back | a, o, u | | Neutral | e, i |

Rule: Within a single word stem, front and back vowels NEVER mix. Suffixes have front/back variants and must match the stem:

| Stem | Suffix (inessive "in") | Result | |------|-----------------------|--------| | talo (back vowels) | -ssa | talossa "in the house" | | metsä (front vowels) | -ssä | metsässä "in the forest" | | työ (front vowels) | -ssä | työssä "at work" | | pöytä (front vowels) | -ssä | pöydässä "on the table" (with gradation) |

Suffix pairs with front/back variants:

| Back | Front | Meaning | |------|-------|---------| | -ssa | -ssä | inessive (in) | | -sta | -stä | elative (out of) | | -lla | -llä | adessive (at/on) | | -lta | -ltä | ablative (from) | | -a | -ä | partitive | | -na | -nä | essive | | -tta | -ttä | abessive |

Neutral vowels (e, i) don't determine harmony — they can coexist with either class. But if a word has ONLY neutral vowels (televisio, tie, kieli), it takes front suffixes by default (televisiossa, tiellä, kielessä).

| Wrong | Correct | Reason | |-------|---------|--------| | järjestelmassa | järjestelmässä | front-vowel stem → front suffix | | kansiössä | kansiossa | back-vowel stem → back suffix | | työssä (correct) | työssä | front vowels ö, e → front suffix | | autolla (correct) | autolla | back vowels a, o → back suffix |

Compound words: each part of a compound keeps its own harmony. työ-paikka is fine because each component is internally harmonic, but suffixes attach to the LAST component: työpaikalla (adessive based on -paikka back vowels — wait, both have neutral; but paikka is back-vowel-dominant → -lla).

D. Partitive case — the defining Finnish feature (severity 2.5)

Partitive (-a/-ä/-ta/-tä/-ja/-jä) is used for:

1. Partial / indefinite quantities: kahvia "some coffee", vettä "some water"
2. Counted nouns ≥2 (see rule A): viisi tiedostoa "five files"
3. Negative direct objects: En näe taloa "I don't see a/the house" (NOT taloa → talon)
4. Incomplete / ongoing actions: Luen kirjaa "I'm reading a book (ongoing)" vs Luin kirjan "I read the book (completed)"
5. Object of certain verbs (verb-governed — see rule F below): auttaa käyttäjää, etsiä tiedostoa, rakastaa sinua
6. After certain numerals and quantifiers: paljon ihmisiä "many people", vähän aikaa "little time"
7. In existential sentences with mass/indef quantity: Maitoa on jääkaapissa "There's milk in the fridge"

Partitive vs accusative (genitive) for direct object — the completeness distinction:

| Sentence | Object case | Meaning | |----------|-------------|---------| | Söin omenan. | accusative (= genitive form) | I ate the/an apple (completely). | | Söin omenaa. | partitive | I was eating the/an apple (ongoing/partial). | | Luin kirjan. | accusative | I read the book (finished). | | Luin kirjaa. | partitive | I was reading the book (ongoing). |

This is one of the hardest features for non-Finns — aspect/completeness is grammaticalized.

E. Consonant gradation (astevaihtelu) (severity 1.5)

When adding case suffixes, certain root consonants alternate between strong and weak grade. This happens in many but not all case forms.

Quantitative gradation (doubled → single):

| Strong | Weak | Example | |--------|------|---------| | kk | k | sukka → sukan (sock), tukki → tukin | | pp | p | kuppi → kupin (cup), kauppa → kaupan | | tt | t | matto → maton (carpet), katti → katin |

Qualitative gradation (single → other or zero):

| Strong | Weak | Example | |--------|------|---------| | k | Ø or v | jalka → jalan (foot), aika → ajan, luku → luvun | | t | d | katu → kadun (street), pata → padan | | p | v | apu → avun (help), tapa → tavan | | mp | mm | lampi → lammen (pond) | | nt | nn | kanta → kannan (heel) | | lt | ll | kulta → kullan (gold) | | rt | rr | kerta → kerran (time/instance) | | nk | ng | Helsinki → Helsingin (note: spelled ng in weak grade) |

Gradation triggers: closed-syllable cases (genitive -n, inessive -ssa, etc.) typically use the weak grade. Open-syllable cases (illative, partitive, essive) often keep the strong grade. Plurals and certain endings reverse this.

Worked example with tiedosto (file):

| Case | Form | Note | |------|------|------| | Nominative | tiedosto | no gradation (no consonant cluster to gradate) | | Genitive | tiedoston | (no gradation here, only suffixation) | | Partitive | tiedostoa | strong stem | | Inessive | tiedostossa | | | Illative | tiedostoon | |

Worked example with kauppa (shop) — has gradation:

| Case | Form | Grade | |------|------|-------| | Nominative | kauppa | strong (pp) | | Genitive | kaupan | weak (p) | | Partitive | kauppaa | strong (pp) | | Inessive | kaupassa | weak (p) | | Illative | kauppaan | strong (pp) |

F. Verb-governed case (severity 2.0)

Each Finnish verb dictates which case its object/complement takes. The

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Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: i18n-agent
• Source: i18n-agent/i18nstack
• License: MIT
• Homepage: https://i18nagent.ai

Install and usage instructions live in the source repository linked above.