1 files changed, 88 insertions, 0 deletions
diff --git a/internal/i18n/i18n_test.go b/internal/i18n/i18n_test.go
new file mode 100644
index 0000000..2a6a617
--- /dev/null
+++ b/internal/i18n/i18n_test.go
@@ -0,0 +1,88 @@
+package i18n
+
+import (
+	"testing"
+	"time"
+
+	"github.com/lukaszkasprzak/prognosis/internal/config"
+)
+
+func TestForFallsBackToEnglish(t *testing.T) {
+	if For("klingon").Lang() != EN {
+		t.Fatal("an unknown language must degrade to English, not to empty strings")
+	}
+	if For("pl").Lang() != PL {
+		t.Fatal("pl must resolve to the Polish catalogue")
+	}
+}
+
+// Every catalogue must cover every column, or a table in that language would
+// silently fall back to the internal column name.
+func TestEveryLanguageCoversEveryColumn(t *testing.T) {
+	for _, lang := range []Lang{EN, PL} {
+		c := For(string(lang))
+		for _, col := range config.ValidColumns() {
+			if _, ok := c.headers[col]; !ok {
+				t.Errorf("%s: no header for column %q", lang, col)
+			}
+		}
+	}
+}
+
+// The WMO codes must match across languages: a code described in English but
+// not Polish would print "code 71" to a Polish reader.
+func TestConditionCoverageMatchesAcrossLanguages(t *testing.T) {
+	en, pl := For("en"), For("pl")
+	for code := range en.conditions {
+		if _, ok := pl.conditions[code]; !ok {
+			t.Errorf("code %d described in English but not Polish", code)
+		}
+	}
+	for code := range pl.conditions {
+		if _, ok := en.conditions[code]; !ok {
+			t.Errorf("code %d described in Polish but not English", code)
+		}
+	}
+}
+
+func TestWordAndSpeciesCoverageMatches(t *testing.T) {
+	en, pl := For("en"), For("pl")
+	for k := range en.words {
+		if _, ok := pl.words[k]; !ok {
+			t.Errorf("word %q missing from Polish", k)
+		}
+	}
+	for _, s := range config.AllSpecies {
+		if _, ok := en.species[s]; !ok {
+			t.Errorf("species %q missing from English", s)
+		}
+		if _, ok := pl.species[s]; !ok {
+			t.Errorf("species %q missing from Polish", s)
+		}
+	}
+	for _, b := range []string{"none", "low", "medium", "high", "very high"} {
+		if en.Band(b) == b && b != "none" && b != "low" && b != "medium" && b != "high" && b != "very high" {
+			t.Errorf("band %q missing from English", b)
+		}
+		if pl.Band(b) == b {
+			t.Errorf("band %q not translated to Polish", b)
+		}
+	}
+}
+
+func TestUnknownCodeIsVisible(t *testing.T) {
+	got := For("en").Condition(4242)
+	if got != "code 4242" {
+		t.Fatalf("unknown codes must be visible, got %q", got)
+	}
+}
+
+func TestDate(t *testing.T) {
+	d := time.Date(2026, 8, 10, 13, 0, 0, 0, time.UTC) // a Monday
+	if got, want := For("en").Date(d), "Mon 10 Aug"; got != want {
+		t.Errorf("en date = %q, want %q", got, want)
+	}
+	if got, want := For("pl").Date(d), "pn 10 sie"; got != want {
+		t.Errorf("pl date = %q, want %q", got, want)
+	}
+}