| 15 cases instead of prepositions | Finnish has no prepositions for "in/out of/to", but 15 cases: talossa (in the house), talosta (out of the house), taloon (into the house), talolla (at the house). Carry the English or German preposition over literally and the marking is wrong. | Native speakers map the prepositional phrase onto the correct case; the mapping is logged in the checked terminology. |
| Consonant gradation (stem change) | The stem alternates between strong and weak grade: katu "street" → genitive kadun; pankki → pankin; leipä → leivän. The wrong grade produces a non-word. | Native speakers command the gradation and pick the right stem per case and person — morphologically correct. |
| Vowel harmony | Front vowels (ä ö y) and back vowels (a o u) do not mix; endings follow suit: talossa, but metsässä (-ssa/-ssä). A harmony-breaking ending — especially on foreign names — is wrong at once. | Vowel harmony is kept throughout, including on foreign names and loanwords. |
| No gender, no articles | Finnish has no gender and no articles; hän means both "he" and "she". Into German, gender and definiteness must be reconstructed — on a certificate hän does not give the sex away. | Gender and definiteness are inferred from context; on civil-status documents we reconcile the sex with the remaining data. |
| Length-critical double letters | Vowel and consonant length is written by doubling and carries meaning: tuli "fire" vs tuuli "wind"; tapan "I kill" vs tapaan "I meet". One letter too many or too few changes the word. | Native speakers set the length exactly; critical words are logged in the terminology and cross-checked. |
| Agglutination | Finnish stacks endings: talo+ssa+ni+kin = talossanikin "also in my house". A single Finnish word is often a whole German clause; split wrongly, meaning is lost. | The morphology is resolved by meaning rather than character by character — decomposed correctly and spelled out in German. |
| Foreign names & abbreviations with linking marks | Names and abbreviations take case endings joined by a colon or apostrophe: USA:n, EU:ssa, show'n, Bordeaux'hon. On contracts the ending must not mangle a company name. | Endings are set with colon/apostrophe per Finnish norm; the name stem stays clearly recognisable. |