chore(subscription): localize slack notification messages (#2778)

* chore: translate the slack notification

The feature stale, experiment running and MAU count notifications were
sent in Japanese regardless of the recipient's language setting. Only
the domain event notification honored it.

Move the hardcoded Japanese strings into the locale bundle and pass the
existing localizer (built from Recipient.Language in notify()) down to
the three remaining attachment builders. This also covers the days-left
line of the experiment list, which was inlined in slack.go rather than
in message.go.

message.go is removed since localizedMessage() has no callers left.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* refactor(locale): add Template suffix to templated notification constants

The Template suffix marks message IDs that must be resolved with
MustLocalizeWithTemplate. Every other templated constant in this file
follows it, so align the three subscription notification keys that take
a template field.

NotificationExperimentRunning keeps no suffix since it has no
placeholder and is resolved with MustLocalize.

Only the Go identifiers change; the message IDs and the localized data
are untouched.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

* fix(locale): use count-neutral wording for the experiment days-left message

Address review comments on PR #2778:
- "{{ .Field_1 }} days left" rendered "`1` days left" for an experiment
  with exactly one day remaining. Reword it as "Days left: {{ .Field_1 }}"
  so the English notification is grammatical for singular, plural, zero
  and negative values, and update the test expectation accordingly.

The Japanese message is already count-neutral and stays unchanged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

---------

Co-authored-by: s35560 <s35560@cyberagent.email>
Co-authored-by: Claude Opus 5 <noreply@anthropic.com>

Author: 3 people

pkg/locale/localizedata/en.yaml

@@ -149,4 +149,13 @@ ValueUpdated: "{{ .Field_1 }} value has been updated"
 Cancelled: "{{ .Field_1 }} has been cancelled"
 Failed: "{{ .Field_1 }} has failed"
 Skipped: "{{ .Field_1 }} has been skipped"
-AppliedNow: "{{ .Field_1 }} has been applied immediately"
+AppliedNow: "{{ .Field_1 }} has been applied immediately"
+
+#############################
+# Subscription Notifications
+#############################
+
+NotificationFeatureStale: "There are feature flags that have not been used for more than {{ .Field_1 }} days."
+NotificationExperimentRunning: "There are running experiments."
+NotificationExperimentDaysLeft: "Days left: {{ .Field_1 }}"
+NotificationMAUCount: "This is the MAU for month {{ .Field_1 }}."

pkg/locale/localizedata/ja.yaml

@@ -149,4 +149,13 @@ ValueUpdated: "{{ .Field_1 }}の値が更新されました"
 Cancelled: "{{ .Field_1 }}がキャンセルされました"
 Failed: "{{ .Field_1 }}が失敗しました"
 Skipped: "{{ .Field_1 }}がスキップされました"
-AppliedNow: "{{ .Field_1 }}が即時適用されました"
+AppliedNow: "{{ .Field_1 }}が即時適用されました"
+
+#############################
+# Subscription Notifications
+#############################
+
+NotificationFeatureStale: "{{ .Field_1 }}日以上使用されていないフィーチャーフラグがあります。"
+NotificationExperimentRunning: "実行中のエクスペリメントがあります。"
+NotificationExperimentDaysLeft: "残り {{ .Field_1 }} 日"
+NotificationMAUCount: "{{ .Field_1 }}月のMAUです。"

pkg/locale/localizer.go

@@ -173,6 +173,14 @@ const (
 	AppliedNowTemplate             = "AppliedNow"
 )
 
+// subscription notifications
+const (
+	NotificationFeatureStaleTemplate       = "NotificationFeatureStale"
+	NotificationExperimentRunning          = "NotificationExperimentRunning"
+	NotificationExperimentDaysLeftTemplate = "NotificationExperimentDaysLeft"
+	NotificationMAUCountTemplate           = "NotificationMAUCount"
+)
+
 func init() {
 	bundle = i18n.NewBundle(language.English)
 	bundle.RegisterUnmarshalFunc("yaml", yaml.Unmarshal)

pkg/subscription/sender/notifier/message.go

@@ -19,6 +19,7 @@ import (
 	"encoding/json"
 	"errors"
 	"fmt"
+	"strconv"
 	"time"
 
 	"github.com/slack-go/slack"
@@ -174,11 +175,11 @@ func (n *slackNotifier) createAttachment(
 	case senderproto.Notification_DomainEvent:
 		return n.createDomainEventAttachment(notification.DomainEventNotification, localizer)
 	case senderproto.Notification_FeatureStale:
-		return n.createFeatureStaleAttachment(notification.FeatureStaleNotification)
+		return n.createFeatureStaleAttachment(notification.FeatureStaleNotification, localizer)
 	case senderproto.Notification_ExperimentRunning:
-		return n.createExperimentRunningAttachment(notification.ExperimentRunningNotification)
+		return n.createExperimentRunningAttachment(notification.ExperimentRunningNotification, localizer)
 	case senderproto.Notification_MauCount:
-		return n.createMAUCountAttachment(notification.MauCountNotification)
+		return n.createMAUCountAttachment(notification.MauCountNotification, localizer)
 	case senderproto.Notification_DemoOrganizationCreation:
 		return n.createDemoOrganizationCreationAttachment(notification.DemoOrganizationCreationNotification)
 	}
@@ -257,6 +258,7 @@ func (n *slackNotifier) createDomainEventAttachment(
 
 func (n *slackNotifier) createFeatureStaleAttachment(
 	notification *senderproto.FeatureStaleNotification,
+	localizer locale.Localizer,
 ) (*slack.Attachment, error) {
 	featureListMsg := ""
 	for _, feature := range notification.Features {
@@ -272,16 +274,14 @@ func (n *slackNotifier) createFeatureStaleAttachment(
 		newLine := "- ID: `" + feature.Id + "`, Name: *" + fmt.Sprintf(linkTemplate, url, feature.Name) + "*\n"
 		featureListMsg = featureListMsg + newLine
 	}
-	// handle loc if multi-lang is necessary
-	msg, err := localizedMessage(msgTypeFeatureStale, locale.Ja)
-	if err != nil {
-		return nil, err
-	}
-	replacedMsg := fmt.Sprintf(msg.Message, featuredomain.SecondsToStale/24/60/60)
+	msg := localizer.MustLocalizeWithTemplate(
+		locale.NotificationFeatureStaleTemplate,
+		strconv.Itoa(featuredomain.SecondsToStale/24/60/60),
+	)
 	attachment := &slack.Attachment{
 		Color:      "#F4D03F",
 		MarkdownIn: []string{"text"},
-		Text: replacedMsg + "\n\n" +
+		Text: msg + "\n\n" +
 			"Environment: " + notification.EnvironmentName + "\n\n" +
 			"Feature flags: \n\n" +
 			featureListMsg,
@@ -291,6 +291,7 @@ func (n *slackNotifier) createFeatureStaleAttachment(
 
 func (n *slackNotifier) createExperimentRunningAttachment(
 	notification *senderproto.ExperimentRunningNotification,
+	localizer locale.Localizer,
 ) (*slack.Attachment, error) {
 	listMsg := ""
 	now := time.Now()
@@ -305,18 +306,18 @@ func (n *slackNotifier) createExperimentRunningAttachment(
 			return nil, err
 		}
 		nameLink := fmt.Sprintf(linkTemplate, url, e.Name)
-		newLine := fmt.Sprintf("- 残り `%d` 日, Name: *%s*\n", lastDays(now, time.Unix(e.StopAt, 0)), nameLink)
+		daysLeft := localizer.MustLocalizeWithTemplate(
+			locale.NotificationExperimentDaysLeftTemplate,
+			fmt.Sprintf("`%d`", lastDays(now, time.Unix(e.StopAt, 0))),
+		)
+		newLine := fmt.Sprintf("- %s, Name: *%s*\n", daysLeft, nameLink)
 		listMsg = listMsg + newLine
 	}
-	// handle loc if multi-lang is necessary
-	msg, err := localizedMessage(msgTypeExperimentResult, locale.Ja)
-	if err != nil {
-		return nil, err
-	}
+	msg := localizer.MustLocalize(locale.NotificationExperimentRunning)
 	attachment := &slack.Attachment{
 		Color:      "#3498DB",
 		MarkdownIn: []string{"text"},
-		Text: msg.Message + "\n\n" +
+		Text: msg + "\n\n" +
 			"Environment: " + notification.EnvironmentName + "\n\n" +
 			"Experiments: \n\n" +
 			listMsg,
@@ -326,17 +327,17 @@ func (n *slackNotifier) createExperimentRunningAttachment(
 
 func (n *slackNotifier) createMAUCountAttachment(
 	notification *senderproto.MauCountNotification,
+	localizer locale.Localizer,
 ) (*slack.Attachment, error) {
-	msg, err := localizedMessage(msgTypeMAUCount, locale.Ja)
-	if err != nil {
-		return nil, err
-	}
-	replacedMsg := fmt.Sprintf(msg.Message, notification.Month)
+	msg := localizer.MustLocalizeWithTemplate(
+		locale.NotificationMAUCountTemplate,
+		strconv.Itoa(int(notification.Month)),
+	)
 	p := message.NewPrinter(language.English)
 	attachment := &slack.Attachment{
 		Color:      "#3498DB",
 		MarkdownIn: []string{"text"},
-		Text: replacedMsg + "\n\n" +
+		Text: msg + "\n\n" +
 			"Environment: " + notification.EnvironmentName + "\n" +
 			p.Sprintf("Event count: %d", notification.EventCount) + "\n" +
 			p.Sprintf("User count: %d", notification.UserCount),

pkg/subscription/sender/notifier/slack.go

@@ -16,15 +16,19 @@ package notifier
 
 import (
 	"context"
+	"strconv"
 	"testing"
 	"time"
 
 	"github.com/stretchr/testify/assert"
 	"go.uber.org/zap"
 	"google.golang.org/grpc/metadata"
 
+	featuredomain "github.com/bucketeer-io/bucketeer/v2/pkg/feature/domain"
 	"github.com/bucketeer-io/bucketeer/v2/pkg/locale"
 	domainproto "github.com/bucketeer-io/bucketeer/v2/proto/event/domain"
+	experimentproto "github.com/bucketeer-io/bucketeer/v2/proto/experiment"
+	featureproto "github.com/bucketeer-io/bucketeer/v2/proto/feature"
 	senderproto "github.com/bucketeer-io/bucketeer/v2/proto/subscription/sender"
 )
 
@@ -136,3 +140,140 @@ func TestCreateDomainEventAttachment(t *testing.T) {
 		})
 	}
 }
+
+func newTestLocalizer(lang string) locale.Localizer {
+	md := metadata.New(map[string]string{"accept-language": lang})
+	return locale.NewLocalizer(metadata.NewIncomingContext(context.Background(), md))
+}
+
+func TestCreateFeatureStaleAttachment(t *testing.T) {
+	t.Parallel()
+
+	staleDays := strconv.Itoa(featuredomain.SecondsToStale / 24 / 60 / 60)
+
+	patterns := []struct {
+		desc         string
+		lang         string
+		expectedText string
+	}{
+		{
+			desc:         "english",
+			lang:         locale.En,
+			expectedText: "There are feature flags that have not been used for more than " + staleDays + " days.",
+		},
+		{
+			desc:         "japanese",
+			lang:         locale.Ja,
+			expectedText: staleDays + "日以上使用されていないフィーチャーフラグがあります。",
+		},
+	}
+
+	for _, p := range patterns {
+		t.Run(p.desc, func(t *testing.T) {
+			t.Parallel()
+			notifier := &slackNotifier{webURL: "https://example.com", logger: zap.NewNop()}
+			attachment, err := notifier.createFeatureStaleAttachment(
+				&senderproto.FeatureStaleNotification{
+					EnvironmentName:    "test-env",
+					EnvironmentUrlCode: "test",
+					Features: []*featureproto.Feature{
+						{Id: "feature-id-1", Name: "feature-name-1"},
+					},
+				},
+				newTestLocalizer(p.lang),
+			)
+			assert.NoError(t, err)
+			assert.Contains(t, attachment.Text, p.expectedText)
+			assert.Contains(t, attachment.Text, "https://example.com/test/features/feature-id-1")
+		})
+	}
+}
+
+func TestCreateExperimentRunningAttachment(t *testing.T) {
+	t.Parallel()
+
+	patterns := []struct {
+		desc            string
+		lang            string
+		expectedText    string
+		expectedDaysMsg string
+	}{
+		{
+			desc:            "english",
+			lang:            locale.En,
+			expectedText:    "There are running experiments.",
+			expectedDaysMsg: "- Days left: `1`, Name: *",
+		},
+		{
+			desc:            "japanese",
+			lang:            locale.Ja,
+			expectedText:    "実行中のエクスペリメントがあります。",
+			expectedDaysMsg: "- 残り `1` 日, Name: *",
+		},
+	}
+
+	for _, p := range patterns {
+		t.Run(p.desc, func(t *testing.T) {
+			t.Parallel()
+			notifier := &slackNotifier{webURL: "https://example.com", logger: zap.NewNop()}
+			attachment, err := notifier.createExperimentRunningAttachment(
+				&senderproto.ExperimentRunningNotification{
+					EnvironmentName:    "test-env",
+					EnvironmentUrlCode: "test",
+					Experiments: []*experimentproto.Experiment{
+						{
+							Id:     "experiment-id-1",
+							Name:   "experiment-name-1",
+							StopAt: time.Now().Add(25 * time.Hour).Unix(),
+						},
+					},
+				},
+				newTestLocalizer(p.lang),
+			)
+			assert.NoError(t, err)
+			assert.Contains(t, attachment.Text, p.expectedText)
+			assert.Contains(t, attachment.Text, p.expectedDaysMsg)
+		})
+	}
+}
+
+func TestCreateMAUCountAttachment(t *testing.T) {
+	t.Parallel()
+
+	patterns := []struct {
+		desc         string
+		lang         string
+		expectedText string
+	}{
+		{
+			desc:         "english",
+			lang:         locale.En,
+			expectedText: "This is the MAU for month 4.",
+		},
+		{
+			desc:         "japanese",
+			lang:         locale.Ja,
+			expectedText: "4月のMAUです。",
+		},
+	}
+
+	for _, p := range patterns {
+		t.Run(p.desc, func(t *testing.T) {
+			t.Parallel()
+			notifier := &slackNotifier{webURL: "https://example.com", logger: zap.NewNop()}
+			attachment, err := notifier.createMAUCountAttachment(
+				&senderproto.MauCountNotification{
+					EnvironmentName: "test-env",
+					EventCount:      1234,
+					UserCount:       567,
+					Month:           4,
+				},
+				newTestLocalizer(p.lang),
+			)
+			assert.NoError(t, err)
+			assert.Contains(t, attachment.Text, p.expectedText)
+			assert.Contains(t, attachment.Text, "Event count: 1,234")
+			assert.Contains(t, attachment.Text, "User count: 567")
+		})
+	}
+}