Add Italian (it) language support

[andreabedini]

Hi all,

I am big fan of this project. My father has spent his whole career in the public administration and Catala has gifted us the beautiful afternoons spent discussing the project and the ideas behind it.

I allowed myself to work on a Italian translation. Admittedly it has been mostly developed with Claude Code but hey, AI is good at translations! No harm done if you don't accept AI contributions but, in case something technical is wrong let me know and I'll jump to fix it.

Summary

• Adds Italian surface syntax (lexer_it.cppo.ml) with full keyword set including literate formatting support
• Adds Italian test equivalents for French language-specific tests (money literals, date rounding, exception UTF-8, type token disambiguation)
• Adds Italian localised standard library (stdlib_it, date_it, decimal_it, duration_it, integer_it, list_it, money_it, monthyear_it, period_it)
• Enables Italian in has_localised_stdlib and fixes .catala_it file extension lookup in module resolution (parser_driver.ml)

Italian keyword conflicts handled: anno (YEAR), a (TO), contiene (CONTAINS) cannot be used as identifiers, so affected stdlib names were adapted (e.g. da_anno_mese_giorno uses n_anno, money_it uses montante, period_it renames contiene → data_nel_periodo).

Test plan

• clerk test tests/ — all 673 tests pass
• clerk test tests/stdlib/ — all 21 stdlib tests pass
• Italian-specific tests: literal_parsing_it, rounding_option_it (good/bad), condizioni_utf8, token_tipi

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Adds Italian (it) as a first-class locale variant in the Catala toolchain, including surface syntax, localised stdlib, and regression tests, so Italian .catala_it(.md) sources can be parsed/typechecked/executed and rendered in literate outputs.

Changes:

• Added an Italian surface lexer and wired it into the parser driver/build (Lexer_it, .catala_it extension support).
• Introduced an Italian-localised standard library (Stdlib_it plus date/decimal/duration/integer/list/money/monthyear/period modules).
• Added Italian equivalents of several language-specific regression tests (money literal parsing, date rounding mode behavior, UTF-8 exception labels/conditions, type-token disambiguation) and updated user-facing printers/literate strings for it.

Reviewed changes

Copilot reviewed 26 out of 26 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tests/typing/good/token_tipi.catala_it	New Italian regression test for type-token lexing/disambiguation.
tests/money/good/literal_parsing_it.catala_it	New Italian test for money literal parsing/printing with € and , decimals.
tests/exception/good/condizioni_utf8.catala_it	New Italian test exercising UTF-8 conditions/labels with the Exceptions command output.
tests/date/good/rounding_option_it.catala_it	New Italian “good” test for date rounding mode behavior.
tests/date/bad/rounding_option_it.catala_it	New Italian “bad” test ensuring ambiguous date computations error without rounding mode.
stdlib/stdlib_it.catala_it	New Italian stdlib root module wiring the Italian submodules.
stdlib/date_it.catala_it	Italian Date module (localized API + bindings to Date_internal).
stdlib/decimal_it.catala_it	Italian Decimal helper module.
stdlib/duration_it.catala_it	Italian Duration helper module.
stdlib/integer_it.catala_it	Italian Integer helper module.
stdlib/list_it.catala_it	Italian List helper module.
stdlib/money_it.catala_it	Italian Money helper module (Euro formatting-oriented naming).
stdlib/monthyear_it.catala_it	Italian MonthYear helper module (uses n_anno to avoid keyword conflicts).
stdlib/period_it.catala_it	Italian Period helper module (renames contiene to data_nel_periodo).
compiler/surface/lexer_it.mli	Declares the Italian localised lexer interface.
compiler/surface/lexer_it.cppo.ml	Defines Italian keyword set + lexer macros (including literate directives).
compiler/surface/dune	Builds and preprocesses the Italian lexer as part of the surface library.
compiler/surface/parser_driver.ml	Enables Italian parsing/lexing and .catala_it(.md) extension resolution.
compiler/shared_ast/print.ml	Adds Italian number separators, boolean literals, money suffix, duration units, and injection “content” keyword.
compiler/plugins/explain.ml	Makes explain plugin language selection exhaustive by handling It (fallbacking to English strings).
compiler/literate/literate_common.ml	Adds Italian literate document strings + language extension mapping.
compiler/literate/latex.ml	Supports Italian LaTeX language selection and metadata label.
compiler/literate/html.ml	Adds Italian label for the table of contents.
compiler/catala_utils/global.mli	Extends backend_lang with It.
compiler/catala_utils/global.ml	Extends backend_lang with It and enables localised stdlib for Italian.
compiler/catala_utils/cli.ml	Adds it language code and .catala_it(.md) extension inference.

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[denismerigoux]

Thanks very much @andreabedini for this PR! It looks quite complete and comes with tests, which is very nice. Would you be OK to commit as a maintainer of this Italian translation of Catala? We would want to ping you in the future anytime we change something that requires a new Italian translation. This includes changes to the standard library which are bound to happen quite often.

@vincent-botbol what's needed on top of this PR to add a new language supported by the VSCode plugin? We may want to add these extra steps to https://github.com/CatalaLang/catala/blob/master/CONTRIBUTING.md#contribution-example-internationalization-of-the-catala-syntax

[AltGr]

Note that I have ongoing changes (#1031) that will conflict with this 😬
While the contribution is very nice, I am a bit wary of taking the burden to maintain generated code. We do have ideas to make the addition of languages much simpler though.

[andreabedini]

@denismerigoux sure, I can do that. @AltGr no rush, I can rebase when you are done.

Nevertheless I feel I need to sit in front of a longer source code written in Italian, the translation might still be improved.