diff --git a/modules/context/context.go b/modules/context/context.go
index 47ad310b09..8a94e958b5 100644
--- a/modules/context/context.go
+++ b/modules/context/context.go
@@ -157,7 +157,6 @@ func Contexter() func(next http.Handler) http.Handler {
 			ctx.Data["Context"] = ctx // TODO: use "ctx" in template and remove this
 			ctx.Data["CurrentURL"] = setting.AppSubURL + req.URL.RequestURI()
 			ctx.Data["Link"] = ctx.Link
-			ctx.Data["locale"] = ctx.Locale
 
 			// PageData is passed by reference, and it will be rendered to `window.config.pageData` in `head.tmpl` for JavaScript modules
 			ctx.PageData = map[string]any{}
diff --git a/routers/common/errpage.go b/routers/common/errpage.go
index 9c8ccc3388..923421a29c 100644
--- a/routers/common/errpage.go
+++ b/routers/common/errpage.go
@@ -9,6 +9,7 @@ import (
 
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/base"
+	"code.gitea.io/gitea/modules/context"
 	"code.gitea.io/gitea/modules/httpcache"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
@@ -35,20 +36,18 @@ func RenderPanicErrorPage(w http.ResponseWriter, req *http.Request, err any) {
 	httpcache.SetCacheControlInHeader(w.Header(), 0, "no-transform")
 	w.Header().Set(`X-Frame-Options`, setting.CORSConfig.XFrameOptions)
 
-	data := middleware.GetContextData(req.Context())
-	if data["locale"] == nil {
-		data = middleware.CommonTemplateContextData()
-		data["locale"] = middleware.Locale(w, req)
-	}
+	tmplCtx := context.TemplateContext{}
+	tmplCtx["Locale"] = middleware.Locale(w, req)
+	ctxData := middleware.GetContextData(req.Context())
 
 	// This recovery handler could be called without Gitea's web context, so we shouldn't touch that context too much.
 	// Otherwise, the 500-page may cause new panics, eg: cache.GetContextWithData, it makes the developer&users couldn't find the original panic.
-	user, _ := data[middleware.ContextDataKeySignedUser].(*user_model.User)
+	user, _ := ctxData[middleware.ContextDataKeySignedUser].(*user_model.User)
 	if !setting.IsProd || (user != nil && user.IsAdmin) {
-		data["ErrorMsg"] = "PANIC: " + combinedErr
+		ctxData["ErrorMsg"] = "PANIC: " + combinedErr
 	}
 
-	err = templates.HTMLRenderer().HTML(w, http.StatusInternalServerError, string(tplStatus500), data, nil)
+	err = templates.HTMLRenderer().HTML(w, http.StatusInternalServerError, string(tplStatus500), ctxData, tmplCtx)
 	if err != nil {
 		log.Error("Error occurs again when rendering error page: %v", err)
 		w.WriteHeader(http.StatusInternalServerError)
diff --git a/routers/common/errpage_test.go b/routers/common/errpage_test.go
index 58a633b2a4..4fd63ba49e 100644
--- a/routers/common/errpage_test.go
+++ b/routers/common/errpage_test.go
@@ -26,6 +26,7 @@ func TestRenderPanicErrorPage(t *testing.T) {
 	respContent := w.Body.String()
 	assert.Contains(t, respContent, `class="page-content status-page-500"`)
 	assert.Contains(t, respContent, `</html>`)
+	assert.Contains(t, respContent, `lang="en-US"`) // make sure the locale work
 
 	// the 500 page doesn't have normal pages footer, it makes it easier to distinguish a normal page and a failed page.
 	// especially when a sub-template causes page error, the HTTP response code is still 200,
diff --git a/services/mailer/mail.go b/services/mailer/mail.go
index 0210128046..1f139d233f 100644
--- a/services/mailer/mail.go
+++ b/services/mailer/mail.go
@@ -26,7 +26,6 @@ import (
 	"code.gitea.io/gitea/modules/markup"
 	"code.gitea.io/gitea/modules/markup/markdown"
 	"code.gitea.io/gitea/modules/setting"
-	"code.gitea.io/gitea/modules/templates"
 	"code.gitea.io/gitea/modules/timeutil"
 	"code.gitea.io/gitea/modules/translation"
 	incoming_payload "code.gitea.io/gitea/services/mailer/incoming/payload"
@@ -68,15 +67,12 @@ func SendTestMail(email string) error {
 func sendUserMail(language string, u *user_model.User, tpl base.TplName, code, subject, info string) {
 	locale := translation.NewLocale(language)
 	data := map[string]any{
+		"locale":            locale,
 		"DisplayName":       u.DisplayName(),
 		"ActiveCodeLives":   timeutil.MinutesToFriendly(setting.Service.ActiveCodeLives, locale),
 		"ResetPwdCodeLives": timeutil.MinutesToFriendly(setting.Service.ResetPwdCodeLives, locale),
 		"Code":              code,
 		"Language":          locale.Language(),
-		// helper
-		"locale":    locale,
-		"Str2html":  templates.Str2html,
-		"DotEscape": templates.DotEscape,
 	}
 
 	var content bytes.Buffer
@@ -119,15 +115,12 @@ func SendActivateEmailMail(u *user_model.User, email *user_model.EmailAddress) {
 	}
 	locale := translation.NewLocale(u.Language)
 	data := map[string]any{
+		"locale":          locale,
 		"DisplayName":     u.DisplayName(),
 		"ActiveCodeLives": timeutil.MinutesToFriendly(setting.Service.ActiveCodeLives, locale),
 		"Code":            u.GenerateEmailActivateCode(email.Email),
 		"Email":           email.Email,
 		"Language":        locale.Language(),
-		// helper
-		"locale":    locale,
-		"Str2html":  templates.Str2html,
-		"DotEscape": templates.DotEscape,
 	}
 
 	var content bytes.Buffer
@@ -152,13 +145,10 @@ func SendRegisterNotifyMail(u *user_model.User) {
 	locale := translation.NewLocale(u.Language)
 
 	data := map[string]any{
+		"locale":      locale,
 		"DisplayName": u.DisplayName(),
 		"Username":    u.Name,
 		"Language":    locale.Language(),
-		// helper
-		"locale":    locale,
-		"Str2html":  templates.Str2html,
-		"DotEscape": templates.DotEscape,
 	}
 
 	var content bytes.Buffer
@@ -185,14 +175,11 @@ func SendCollaboratorMail(u, doer *user_model.User, repo *repo_model.Repository)
 
 	subject := locale.Tr("mail.repo.collaborator.added.subject", doer.DisplayName(), repoName)
 	data := map[string]any{
+		"locale":   locale,
 		"Subject":  subject,
 		"RepoName": repoName,
 		"Link":     repo.HTMLURL(),
 		"Language": locale.Language(),
-		// helper
-		"locale":    locale,
-		"Str2html":  templates.Str2html,
-		"DotEscape": templates.DotEscape,
 	}
 
 	var content bytes.Buffer
@@ -259,6 +246,7 @@ func composeIssueCommentMessages(ctx *mailCommentContext, lang string, recipient
 	locale := translation.NewLocale(lang)
 
 	mailMeta := map[string]any{
+		"locale":          locale,
 		"FallbackSubject": fallback,
 		"Body":            body,
 		"Link":            link,
@@ -275,10 +263,6 @@ func composeIssueCommentMessages(ctx *mailCommentContext, lang string, recipient
 		"ReviewComments":  reviewComments,
 		"Language":        locale.Language(),
 		"CanReply":        setting.IncomingEmail.Enabled && commentType != issues_model.CommentTypePullRequestPush,
-		// helper
-		"locale":    locale,
-		"Str2html":  templates.Str2html,
-		"DotEscape": templates.DotEscape,
 	}
 
 	var mailSubject bytes.Buffer
@@ -469,7 +453,7 @@ func SendIssueAssignedMail(ctx context.Context, issue *issues_model.Issue, doer
 		if err != nil {
 			return err
 		}
-		SendAsyncs(msgs)
+		SendAsync(msgs...)
 	}
 	return nil
 }
diff --git a/services/mailer/mail_issue.go b/services/mailer/mail_issue.go
index baa9f1d9ab..fab3315be2 100644
--- a/services/mailer/mail_issue.go
+++ b/services/mailer/mail_issue.go
@@ -162,7 +162,7 @@ func mailIssueCommentBatch(ctx *mailCommentContext, users []*user_model.User, vi
 			if err != nil {
 				return err
 			}
-			SendAsyncs(msgs)
+			SendAsync(msgs...)
 			receivers = receivers[:i]
 		}
 	}
diff --git a/services/mailer/mail_release.go b/services/mailer/mail_release.go
index 7bc3db3fe6..88973a6be2 100644
--- a/services/mailer/mail_release.go
+++ b/services/mailer/mail_release.go
@@ -14,7 +14,6 @@ import (
 	"code.gitea.io/gitea/modules/markup"
 	"code.gitea.io/gitea/modules/markup/markdown"
 	"code.gitea.io/gitea/modules/setting"
-	"code.gitea.io/gitea/modules/templates"
 	"code.gitea.io/gitea/modules/translation"
 )
 
@@ -69,13 +68,10 @@ func mailNewRelease(ctx context.Context, lang string, tos []string, rel *repo_mo
 
 	subject := locale.Tr("mail.release.new.subject", rel.TagName, rel.Repo.FullName())
 	mailMeta := map[string]any{
+		"locale":   locale,
 		"Release":  rel,
 		"Subject":  subject,
 		"Language": locale.Language(),
-		// helper
-		"locale":    locale,
-		"Str2html":  templates.Str2html,
-		"DotEscape": templates.DotEscape,
 	}
 
 	var mailBody bytes.Buffer
@@ -95,5 +91,5 @@ func mailNewRelease(ctx context.Context, lang string, tos []string, rel *repo_mo
 		msgs = append(msgs, msg)
 	}
 
-	SendAsyncs(msgs)
+	SendAsync(msgs...)
 }
diff --git a/services/mailer/mail_repo.go b/services/mailer/mail_repo.go
index e9c1991b5b..b89dcd43b5 100644
--- a/services/mailer/mail_repo.go
+++ b/services/mailer/mail_repo.go
@@ -12,7 +12,6 @@ import (
 	repo_model "code.gitea.io/gitea/models/repo"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/setting"
-	"code.gitea.io/gitea/modules/templates"
 	"code.gitea.io/gitea/modules/translation"
 )
 
@@ -65,6 +64,7 @@ func sendRepoTransferNotifyMailPerLang(lang string, newOwner, doer *user_model.U
 	}
 
 	data := map[string]any{
+		"locale":      locale,
 		"Doer":        doer,
 		"User":        repo.Owner,
 		"Repo":        repo.FullName(),
@@ -72,10 +72,6 @@ func sendRepoTransferNotifyMailPerLang(lang string, newOwner, doer *user_model.U
 		"Subject":     subject,
 		"Language":    locale.Language(),
 		"Destination": destination,
-		// helper
-		"locale":    locale,
-		"Str2html":  templates.Str2html,
-		"DotEscape": templates.DotEscape,
 	}
 
 	if err := bodyTemplates.ExecuteTemplate(&content, string(mailRepoTransferNotify), data); err != nil {
diff --git a/services/mailer/mail_team_invite.go b/services/mailer/mail_team_invite.go
index 88ad0c9836..ab32beefac 100644
--- a/services/mailer/mail_team_invite.go
+++ b/services/mailer/mail_team_invite.go
@@ -14,7 +14,6 @@ import (
 	"code.gitea.io/gitea/modules/base"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/setting"
-	"code.gitea.io/gitea/modules/templates"
 	"code.gitea.io/gitea/modules/translation"
 )
 
@@ -53,16 +52,13 @@ func MailTeamInvite(ctx context.Context, inviter *user_model.User, team *org_mod
 
 	subject := locale.Tr("mail.team_invite.subject", inviter.DisplayName(), org.DisplayName())
 	mailMeta := map[string]any{
+		"locale":       locale,
 		"Inviter":      inviter,
 		"Organization": org,
 		"Team":         team,
 		"Invite":       invite,
 		"Subject":      subject,
 		"InviteURL":    inviteURL,
-		// helper
-		"locale":    locale,
-		"Str2html":  templates.Str2html,
-		"DotEscape": templates.DotEscape,
 	}
 
 	var mailBody bytes.Buffer
diff --git a/services/mailer/mailer.go b/services/mailer/mailer.go
index 42d7d5ad5d..5e8e3dbb38 100644
--- a/services/mailer/mailer.go
+++ b/services/mailer/mailer.go
@@ -425,15 +425,12 @@ func NewContext(ctx context.Context) {
 	go graceful.GetManager().RunWithCancel(mailQueue)
 }
 
-// SendAsync send mail asynchronously
-func SendAsync(msg *Message) {
-	SendAsyncs([]*Message{msg})
-}
+// SendAsync send emails asynchronously (make it mockable)
+var SendAsync = sendAsync
 
-// SendAsyncs send mails asynchronously
-func SendAsyncs(msgs []*Message) {
+func sendAsync(msgs ...*Message) {
 	if setting.MailService == nil {
-		log.Error("Mailer: SendAsyncs is being invoked but mail service hasn't been initialized")
+		log.Error("Mailer: SendAsync is being invoked but mail service hasn't been initialized")
 		return
 	}
 
diff --git a/templates/status/500.tmpl b/templates/status/500.tmpl
index e5570bde73..edcb90f9a4 100644
--- a/templates/status/500.tmpl
+++ b/templates/status/500.tmpl
@@ -1,12 +1,12 @@
 {{/* This page should only depend the minimal template functions/variables, to avoid triggering new panics.
 * base template functions: AppName, AssetUrlPrefix, AssetVersion, AppSubUrl, ThemeName, Str2html
-* locale
-* Flash
-* ErrorMsg
-* SignedUser (optional)
+* ctx.Locale
+* .Flash
+* .ErrorMsg
+* .SignedUser (optional)
 */}}
 <!DOCTYPE html>
-<html lang="{{.locale.Lang}}" data-theme="{{ThemeName .SignedUser}}">
+<html lang="{{ctx.Locale.Lang}}" data-theme="{{ThemeName .SignedUser}}">
 <head>
 	<meta name="viewport" content="width=device-width, initial-scale=1">
 	<title>Internal Server Error - {{AppName}}</title>
@@ -19,8 +19,8 @@
 		<nav class="ui secondary menu gt-border-secondary-bottom">
 			<div class="ui container gt-df">
 				<div class="item gt-f1">
-					<a href="{{AppSubUrl}}/" aria-label="{{.locale.Tr "home"}}">
-						<img width="30" height="30" src="{{AssetUrlPrefix}}/img/logo.svg" alt="{{.locale.Tr "logo"}}" aria-hidden="true">
+					<a href="{{AppSubUrl}}/" aria-label="{{ctx.Locale.Tr "home"}}">
+						<img width="30" height="30" src="{{AssetUrlPrefix}}/img/logo.svg" alt="{{ctx.Locale.Tr "logo"}}" aria-hidden="true">
 					</a>
 				</div>
 				<div class="item">
@@ -37,12 +37,12 @@
 			<div class="divider"></div>
 			<div class="ui container gt-my-5">
 				{{if .ErrorMsg}}
-					<p>{{.locale.Tr "error.occurred"}}:</p>
+					<p>{{ctx.Locale.Tr "error.occurred"}}:</p>
 					<pre class="gt-whitespace-pre-wrap gt-break-all">{{.ErrorMsg}}</pre>
 				{{end}}
 				<div class="center gt-mt-5">
-					{{if or .SignedUser.IsAdmin .ShowFooterVersion}}<p>{{.locale.Tr "admin.config.app_ver"}}: {{AppVer}}</p>{{end}}
-					{{if .SignedUser.IsAdmin}}<p>{{.locale.Tr "error.report_message" | Str2html}}</p>{{end}}
+					{{if or .SignedUser.IsAdmin .ShowFooterVersion}}<p>{{ctx.Locale.Tr "admin.config.app_ver"}}: {{AppVer}}</p>{{end}}
+					{{if .SignedUser.IsAdmin}}<p>{{ctx.Locale.Tr "error.report_message" | Str2html}}</p>{{end}}
 				</div>
 			</div>
 		</div>