| Noun-class concord broken | Every adjective, numeral and verb must take the noun's class prefix (watu wawili wazuri wamefika). Miss the concord and you write ungrammatical Swahili that any native speaker spots at once. | Native speakers carry the class concord throughout — checked under the ISO 17100 four-eyes principle. |
| German gender mapped onto classes | Swahili has no grammatical gender, but noun classes (m-/wa-, ki-/vi-, m-/mi-). Carry German der/die/das logic across and you put words in the wrong class. | Nouns are assigned to their correct class; the whole concord chain follows from that. |
| Tense prefix confused | Tense sits in the verb prefix: -na- (present), -li- (past), -ta- (future), -me- (perfect). A wrong prefix shifts the time frame — consequential in contracts and certificates. | Tense and aspect prefixes are set correctly and checked against the sense of the source text. |
| Arabic loanwords & register mixed | Many terms come from Arabic (kitabu "book", wakati "time", safari "journey"). Coastal and inland registers differ; the wrong choice reads as out of place. | Native specialists choose register-appropriately and write in standard Swahili (Kiswahili sanifu). |
| Standard vs regional variety confused | Tanzanian/Zanzibari standard Swahili differs from Kenyan or Congolese (Kingwana) registers. An official text in the wrong variety reads as foreign at the destination. | We fix the target variety — usually Kiswahili sanifu — before we start and keep it consistent. |
| Address & honorifics inappropriate | Politeness forms and honorifics (Ndugu, Mzee, Bwana/Bi) and the class-2 respectful form carry social meaning. Chosen wrongly, the text reads as disrespectful in an official or business context. | Register and address are matched to the occasion — formal, official or promotional. |
| Swahili time-reckoning taken literally | The traditional clock starts at sunrise: saa moja ("hour one") is about 7 a.m., not 1 a.m. Carried over literally, a time comes out six hours wrong. | Times are converted correctly between the Swahili and German conventions, not copied character-for-character. |
| Names & Arabic transliteration inconsistent | Names appear transliterated differently (Mohammed/Muhammad; bin/binti "son/daughter of"), historically sometimes in the Arabic Ajami script. Inconsistent transcription disrupts matching in registers. | Names are transcribed consistently and, where they diverge, noted against the passport form. |