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ICU MessageFormat format (.mf, .messageformat)

ICU MessageFormat is the pattern syntax used by ICU and many i18n libraries to express messages with placeholders and grammatical variation. This format treats each input line as one independent MessageFormat pattern.

A plain-text pattern extracts as a single translatable block. A pattern with simple placeholders — {0}, {name}, {name, type}, {name, type, style} — also extracts as a single block, with the placeholders carried as inline runs around the literal text so they cannot be accidentally translated or reordered. A pattern with a plural, select, or selectordinal picker splits into one block per branch body, so each grammatical form can be translated independently; the picker scaffolding ({count, plural, …}, {gender, select, …}) and any text outside the picker is preserved through the skeleton rather than extracted. ICU quoting is decoded before extraction: '' becomes a literal apostrophe and '{…}' protects a literal-brace passage. Java's deprecated choice format is rejected with an error.

IDmessageformat
SourceBuilt-in
Extensions.mf, .messageformat
MIME Typestext/x-messageformat
CapabilitiesRead + Write

This format has no configurable parameters.

Examples

Translate ICU patterns

No configuration is required. Declare the format to extract each line as a pattern, splitting plural and select branches into separate blocks.

format:
  name: messageformat

Processing notes

  • Plain and simple-placeholder patterns extract as one block per line; plural / select / selectordinal patterns extract one block per branch body.

  • Placeholders are represented as inline runs (icu:argument, icu:number for #) so they survive translation intact.

  • Blank lines and trailing newlines round-trip as skeleton; with a skeleton store active, output is byte-exact.

Limitations

  • Each line is parsed as a self-contained pattern; a single pattern spanning multiple lines is not supported.

  • The deprecated ICU choice format is not supported and is reported as an error.

  • There are no configurable parameters; upstream output options such as plural-form expansion or pretty-printing are not exposed.

Reference documentation

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