Refactor i18n to locale (#20153)

* Refactor `i18n` to `locale`

- Currently we're using the `i18n` variable naming for the `locale`
struct. This contains locale's specific information and cannot be used
for general i18n purpose, therefore refactoring it to `locale` makes
more sense.
- Ref: https://github.com/go-gitea/gitea/pull/20096#discussion_r906699200

* Update routers/install/install.go

services/mailer/mail.go

@@ -80,7 +80,7 @@ func sendUserMail(language string, u *user_model.User, tpl base.TplName, code, s
 		"Code":              code,
 		"Language":          locale.Language(),
 		// helper
-		"i18n":      locale,
+		"locale":    locale,
 		"Str2html":  templates.Str2html,
 		"DotEscape": templates.DotEscape,
 	}
@@ -131,7 +131,7 @@ func SendActivateEmailMail(u *user_model.User, email *user_model.EmailAddress) {
 		"Email":           email.Email,
 		"Language":        locale.Language(),
 		// helper
-		"i18n":      locale,
+		"locale":    locale,
 		"Str2html":  templates.Str2html,
 		"DotEscape": templates.DotEscape,
 	}
@@ -162,7 +162,7 @@ func SendRegisterNotifyMail(u *user_model.User) {
 		"Username":    u.Name,
 		"Language":    locale.Language(),
 		// helper
-		"i18n":      locale,
+		"locale":    locale,
 		"Str2html":  templates.Str2html,
 		"DotEscape": templates.DotEscape,
 	}
@@ -196,7 +196,7 @@ func SendCollaboratorMail(u, doer *user_model.User, repo *repo_model.Repository)
 		"Link":     repo.HTMLURL(),
 		"Language": locale.Language(),
 		// helper
-		"i18n":      locale,
+		"locale":    locale,
 		"Str2html":  templates.Str2html,
 		"DotEscape": templates.DotEscape,
 	}
@@ -281,7 +281,7 @@ func composeIssueCommentMessages(ctx *mailCommentContext, lang string, recipient
 		"ReviewComments":  reviewComments,
 		"Language":        locale.Language(),
 		// helper
-		"i18n":      locale,
+		"locale":    locale,
 		"Str2html":  templates.Str2html,
 		"DotEscape": templates.DotEscape,
 	}