feat: add multi-language support

tests/test_i18n.py

@@ -0,0 +1,58 @@
+"""
+SPDX-FileCopyrightText: © Sebastian Thomschke and contributors
+SPDX-License-Identifier: AGPL-3.0-or-later
+SPDX-ArtifactOfProjectHomePage: https://github.com/Second-Hand-Friends/kleinanzeigen-bot/
+"""
+import pytest
+from _pytest.monkeypatch import MonkeyPatch  # pylint: disable=import-private-name
+from kleinanzeigen_bot import i18n
+
+
+@pytest.mark.parametrize("lang, expected", [
+    (None, ("en", "US", "UTF-8")),  # Test with no LANG variable (should default to ("en", "US", "UTF-8"))
+    ("fr", ("fr", None, "UTF-8")),  # Test with just a language code
+    ("fr_CA", ("fr", "CA", "UTF-8")),  # Test with language + region, no encoding
+    ("pt_BR.iso8859-1", ("pt", "BR", "ISO8859-1")),  # Test with language + region + encoding
+])
+def test_detect_locale(monkeypatch: MonkeyPatch, lang: str | None, expected: i18n.Locale) -> None:
+    """
+    Pytest test case to verify detect_system_language() behavior under various LANG values.
+    """
+    # Clear or set the LANG environment variable as needed.
+    if lang is None:
+        monkeypatch.delenv("LANG", raising = False)
+    else:
+        monkeypatch.setenv("LANG", lang)
+
+    # Call the function and compare the result to the expected output.
+    result = i18n._detect_locale()  # pylint: disable=protected-access
+    assert result == expected, f"For LANG={lang}, expected {expected} but got {result}"
+
+
+@pytest.mark.parametrize("lang, noun, count, prefix_with_count, expected", [
+    ("en", "field", 1, True, "1 field"),
+    ("en", "field", 2, True, "2 fields"),
+    ("en", "field", 2, False, "fields"),
+    ("en", "attribute", 2, False, "attributes"),
+    ("en", "bus", 2, False, "buses"),
+    ("en", "city", 2, False, "cities"),
+    ("de", "Feld", 1, True, "1 Feld"),
+    ("de", "Feld", 2, True, "2 Felder"),
+    ("de", "Feld", 2, False, "Felder"),
+    ("de", "Anzeige", 2, False, "Anzeigen"),
+    ("de", "Attribute", 2, False, "Attribute"),
+    ("de", "Bild", 2, False, "Bilder"),
+    ("de", "Datei", 2, False, "Dateien"),
+    ("de", "Kategorie", 2, False, "Kategorien")
+])
+def test_pluralize(
+    lang:str,
+    noun:str,
+    count:int,
+    prefix_with_count:bool,
+    expected: str
+) -> None:
+    i18n.set_current_locale(i18n.Locale(lang, "US", "UTF_8"))
+
+    result = i18n.pluralize(noun, count, prefix_with_count)
+    assert result == expected, f"For LANG={lang}, expected {expected} but got {result}"