Move internal packages to an internal folder

For reference: https://go.dev/doc/go1.4#internalpackages

internal/locale/catalog_test.go

@@ -0,0 +1,90 @@
+// SPDX-FileCopyrightText: Copyright The Miniflux Authors. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+package locale // import "miniflux.app/v2/internal/locale"
+
+import "testing"
+
+func TestParserWithInvalidData(t *testing.T) {
+	_, err := parseTranslationMessages([]byte(`{`))
+	if err == nil {
+		t.Fatal(`An error should be returned when parsing invalid data`)
+	}
+}
+
+func TestParser(t *testing.T) {
+	translations, err := parseTranslationMessages([]byte(`{"k": "v"}`))
+	if err != nil {
+		t.Fatalf(`Unexpected parsing error: %v`, err)
+	}
+
+	if translations == nil {
+		t.Fatal(`Translations should not be nil`)
+	}
+
+	value, found := translations["k"]
+	if !found {
+		t.Fatal(`The translation should contains the defined key`)
+	}
+
+	if value.(string) != "v" {
+		t.Fatal(`The translation key should contains the defined value`)
+	}
+}
+
+func TestLoadCatalog(t *testing.T) {
+	if err := LoadCatalogMessages(); err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestAllKeysHaveValue(t *testing.T) {
+	for language := range AvailableLanguages() {
+		messages, err := loadTranslationFile(language)
+		if err != nil {
+			t.Fatalf(`Unable to load translation messages for language %q`, language)
+		}
+
+		if len(messages) == 0 {
+			t.Fatalf(`The language %q doesn't have any messages`, language)
+		}
+
+		for k, v := range messages {
+			switch value := v.(type) {
+			case string:
+				if value == "" {
+					t.Errorf(`The key %q for the language %q have an empty string as value`, k, language)
+				}
+			case []string:
+				if len(value) == 0 {
+					t.Errorf(`The key %q for the language %q have an empty list as value`, k, language)
+				}
+			}
+		}
+	}
+}
+
+func TestMissingTranslations(t *testing.T) {
+	refLang := "en_US"
+	references, err := loadTranslationFile(refLang)
+	if err != nil {
+		t.Fatal(`Unable to parse reference language`)
+	}
+
+	for language := range AvailableLanguages() {
+		if language == refLang {
+			continue
+		}
+
+		messages, err := loadTranslationFile(language)
+		if err != nil {
+			t.Fatalf(`Parsing error for language %q`, language)
+		}
+
+		for key := range references {
+			if _, found := messages[key]; !found {
+				t.Fatalf(`Translation key %q not found in language %q`, key, language)
+			}
+		}
+	}
+}