src/uu/<utility>/locales/<locale>.ftl — per-utility translations (~100 utilities).
src/uucore/locales/<locale>.ftl — shared strings used across utilities.

en-US.ftl is the source/reference locale in every locales/ directory; every other file (including fr-FR.ftl) is a translation of it.

Note: base32, base64, and basenc share one set of translations — base64/locales and basenc/locales are symlinks to base32/locales.

Editing translations

Each .ftl file is monolingual: a complete set of key = value message definitions.

Change only the right-hand side (the value). Keep the keys identical to en-US.ftl — missing keys fall back to English, extra keys are dead.
Copy placeables such as {$file} or {$count} verbatim; never translate the variable name inside {...}.
Every file must end with a trailing newline.

Don't edit en-US.ftl here: it is overwritten daily from upstream uutils/coreutils. Change the English source strings there instead. French (fr-FR.ftl) is translated here like any other locale — via Weblate or pull requests.

Validating before a pull request

pip install pre-commit moz-fluent-linter

pre-commit run --all-files
moz-fluent-lint --config .github/fluent_linter_config.yml src/uu/

CI runs the same two checks on every push and pull request.