The Turkish I

Turkish and Azerbaijani write four letters where English writes two: dotted i and İ, dotless ı and I. Lower-case i goes with upper-case İ, and ı with I. Unicode keeps this in its special casing table (SpecialCasing.txt), so every case change has two possible answers, depending on whether it uses the locale.

The outputs below come from Node.js 26 and Swift 6.4 on macOS.

Two different mistakes follow from this, and GlobalLingo reports both.

Keys must not follow the locale (TRI001)

Keys are identifiers. Code that changes their case with the device's locale breaks on Turkish and Azerbaijani devices, even in an app that only ships English:

// The server sends "IDLE"; the translation file has "status.idle".
t(`status.${state.toLocaleLowerCase()}`); // on a Turkish device: "status.ıdle", not found
t(`status.${state.toLowerCase()}`); // "status.idle" everywhere
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NSLocalizedString("status.\(name)".localizedLowercase, comment: "") // follows the device
NSLocalizedString("status.\(name)".lowercased(), comment: "") // does not
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fixtures/expo-i18next/App.tsx and fixtures/swiftui-catalog have one each. Keys that contain İ or ı themselves (TRI002) have the same problem from the other side: no case change gives them back.

Text must follow the language (TRI003)

Translated text is the opposite: an upper-case heading in Turkish needs the Turkish mapping, or "Kitap teslim edildi" ("the book was delivered") becomes "KITAP TESLIM EDILDI" instead of "KİTAP TESLİM EDİLDİ", with four wrong letters. GlobalLingo reports a case change right after a lookup when the app ships Turkish or Azerbaijani:

t('pickup.city').toUpperCase(); // TRI003
t('pickup.city').toLocaleUpperCase(i18n.language); // the app's language
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String(localized: "Pickup in \(city)").uppercased() // TRI003
String(localized: "Pickup in \(city)").uppercased(with: locale) // the language of the text
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Dart has no locale-aware toUpperCase() (its documentation: "uses the language independent Unicode mapping and thus only works in some languages"). In Flutter, put the upper-case text in the ARB file as a message of its own, so the Turkish translator writes the dotted capital:

{
  "pickupHeading": "PICKUP IN {city}",
  "@pickupHeading": { "placeholders": { "city": { "type": "String" } } }
}
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The city itself is data; if it must be upper case too, upper-case it where the app knows the language, for example on the server.

Why not just ignore it

Both mistakes pass every test that runs in English, and both are invisible in a simulator set to English. They show up as raw keys or misspelled words for users with a Turkish or Azerbaijani device, which is why GlobalLingo checks the code for them instead of waiting for a screenshot.