• feat(types): parseInterpolation: 'icu' and parseInterpolation: 'mf2' type t() options from the message's ICU MessageFormat arguments (i18next-icu) or MessageFormat 2 variables (i18next-mf2), so ICU and MF2 users no longer need parseInterpolation: false and lose argument checking. Missing, misspelled and wrongly typed arguments fail, and so does leaving out the options for a message with arguments (t('greeting')); that error names the missing arguments. Opt-in, default true is unchanged.
  • ICU: {name} takes string | number, {n, number}, plural and selectordinal take number, {d, date} and {t, time} take Date, select takes its case keys or any string (for other), and arguments nested in cases are required too. # and tags are not arguments, apostrophe quoting is read like intl-messageformat does.
  • MF2: {$name} takes string | number, a variable annotated with :number, :integer, :currency, :percent or :unit (inline or through .input / .local) takes number, :datetime, :date and :time take Date, :string takes string, option and markup variables (minimumFractionDigits=$digits, {#link href=$url}) are required too, .local variables are not arguments, and |quoted literals| and \{ escapes are skipped.
  • interpolationFormatTypeMap overrides a type by ICU format or MF2 function name, e.g. date: Date | number or a custom uppercase: string.
  • Applies to t(), getFixedT(), i18n.t, key prefixes, namespaces, the selector API and react-i18next's Trans values. Messages need literal types, as the resources file from i18next-cli's types command has them.
  • Type-check cost with 1,000 messages and one call each: 1.35s instead of 0.86s with false (TypeScript 6), 0.5s instead of 0.26s with TypeScript 7. Messages that no call uses cost nothing.
• fix(types): with the default (non-strict) key checks, an options object with a missing or misspelled interpolation variable now reports the missing variable (Property 'name' is missing) instead of '{ nmae: string }' is not assignable to type 'string' from the default-value overload.