feat(time): use locale word fallback for relative time

Co-Authored-By: Virgil <virgil@lethean.io>

time.go

@@ -48,11 +48,20 @@ func FormatAgo(count int, unit string) string {
 	key := "time.ago." + unit
 	result := svc.T(key, map[string]any{"Count": count})
 	if result == key {
-		return core.Sprintf("%d %s ago", count, Pluralize(unit, count))
+		return core.Sprintf("%d %s ago", count, fallbackAgoUnit(unit, count))
 	}
 	return result
 }
 
+func fallbackAgoUnit(unit string, count int) string {
+	lang := currentLangForGrammar()
+	rendered := renderWord(lang, unit)
+	if rendered != unit {
+		return rendered
+	}
+	return Pluralize(unit, count)
+}
+
 func normalizeAgoUnit(unit string) string {
 	unit = core.Lower(core.Trim(unit))
 	switch unit {

time_test.go

@@ -245,3 +245,28 @@ func TestFormatAgo_Good_FrenchRelativeTime(t *testing.T) {
 		})
 	}
 }
+
+func TestFormatAgo_FallsBackToLocaleWordMap(t *testing.T) {
+	prev := Default()
+	svc, err := NewWithFS(fstest.MapFS{
+		"en.json": &fstest.MapFile{
+			Data: []byte(`{
+				"gram": {
+					"word": {
+						"month": "mois"
+					}
+				}
+			}`),
+		},
+	}, ".")
+	require.NoError(t, err)
+	SetDefault(svc)
+	t.Cleanup(func() {
+		SetDefault(prev)
+	})
+
+	require.NoError(t, SetLanguage("en"))
+
+	got := FormatAgo(2, "month")
+	assert.Equal(t, "2 mois ago", got)
+}