Plural translation does not work with `tr_n()` and CSV translation IDs

[LavandePotions]

Tested versions

v4.3.stable.flathub [77dcf97]

System information

Pop!_OS 22.04 LTS

Issue description

tr_n() always return Singular Translation even when number_of_coins is superior to 1.

e.g.

# This work
#%BasicLabel.text = tr_n("single coin", "more coins", number_of_coins)
	
# This does not
%BasicLabel.text = tr_n("COIN_LABEL_SINGULAR", "COIN_LABEL_PLURAL", number_of_coins)

Steps to reproduce

In a new project :

1. Add a CSV file with at least two lines (one singular, one plural).

LABEL_SINGULAR,one
LABEL_PLURAL,many

2. Open menu Project -> project settings... -> Localization and import .translation files.
3. Use tr_n() with Singular and Plural Keys.

var tr_string = tr_n("LABEL_SINGULAR", "LABEL_PLURAL", 2)

4. It will always use the Singular key whatever the int value is...

Minimal reproduction project (MRP)

link to the repo
lpGodot_tr_n_issue

[kleonc]

Seems like translations are being imported as OptimizedTranslations for which get_plural_message is not supported/implemented.

In the MRP:

func _ready() -> void:
	for locale: String in TranslationServer.get_loaded_locales():
		var translation: Translation = TranslationServer.get_translation_object(locale)
		prints(locale, translation.get_class())

Output (v4.3.stable.official [77dcf97], v4.4.dev7.official [46c8f8c]):

en OptimizedTranslation
es OptimizedTranslation
fr OptimizedTranslation

Relevant source:

godot/core/string/optimized_translation.cpp

Lines 303 to 306 in 5b52b4b

	StringName OptimizedTranslation::get_plural_message(const StringName &p_src_text, const StringName &p_plural_text, int p_n, const StringName &p_context) const {
	// The use of plurals translation is not yet supported in OptimizedTranslation.
	return get_message(p_src_text, p_context);
	}

For comparison:

godot/core/string/translation_po.cpp

Lines 288 to 312 in d79ff84

	StringName TranslationPO::get_plural_message(const StringName &p_src_text, const StringName &p_plural_text, int p_n, const StringName &p_context) const {
	ERR_FAIL_COND_V_MSG(p_n < 0, StringName(), "N passed into translation to get a plural message should not be negative. For negative numbers, use singular translation please. Search \"gettext PO Plural Forms\" online for the documentation on translating negative numbers.");
	// If the query is the same as last time, return the cached result.
	if (p_n == last_plural_n && p_context == last_plural_context && p_src_text == last_plural_key) {
	return translation_map[p_context][p_src_text][last_plural_mapped_index];
	}
	if (!translation_map.has(p_context) || !translation_map[p_context].has(p_src_text)) {
	return StringName();
	}
	ERR_FAIL_COND_V_MSG(translation_map[p_context][p_src_text].is_empty(), StringName(), vformat("Source text \"%s\" is registered but doesn't have a translation. Please report this bug.", String(p_src_text)));
	int plural_index = _get_plural_index(p_n);
	ERR_FAIL_COND_V_MSG(plural_index < 0 || translation_map[p_context][p_src_text].size() < plural_index + 1, StringName(), "Plural index returned or number of plural translations is not valid. Please report this bug.");
	// Cache result so that if the next entry is the same, we can return directly.
	// _get_plural_index(p_n) can get very costly, especially when evaluating long plural-rule (Arabic)
	last_plural_key = p_src_text;
	last_plural_context = p_context;
	last_plural_n = p_n;
	last_plural_mapped_index = plural_index;
	return translation_map[p_context][p_src_text][plural_index];
	}

[dalexeev]

See also:

• Add plurals support for CSV translation files godot-proposals#1291
• Add CSV plural support #41519