Reset locale on login (#18023)

* Reset locale on login

Fix #18020

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Update routers/web/user/auth.go

Co-authored-by: Gusted <williamzijl7@hotmail.com>

Co-authored-by: Gusted <williamzijl7@hotmail.com>

routers/web/user/auth.go

@@ -101,10 +101,33 @@ func AutoSignIn(ctx *context.Context) (bool, error) {
 		return false, err
 	}
 
+	if err := resetLocale(ctx, u); err != nil {
+		return false, err
+	}
+
 	middleware.DeleteCSRFCookie(ctx.Resp)
 	return true, nil
 }
 
+func resetLocale(ctx *context.Context, u *user_model.User) error {
+	// Language setting of the user overwrites the one previously set
+	// If the user does not have a locale set, we save the current one.
+	if len(u.Language) == 0 {
+		u.Language = ctx.Locale.Language()
+		if err := user_model.UpdateUserCols(db.DefaultContext, u, "language"); err != nil {
+			return err
+		}
+	}
+
+	middleware.SetLocaleCookie(ctx.Resp, u.Language, 0)
+
+	if ctx.Locale.Language() != u.Language {
+		ctx.Locale = middleware.Locale(ctx.Resp, ctx.Req)
+	}
+
+	return nil
+}
+
 func checkAutoLogin(ctx *context.Context) bool {
 	// Check auto-login.
 	isSucceed, err := AutoSignIn(ctx)
@@ -832,6 +855,11 @@ func handleOAuth2SignIn(ctx *context.Context, source *login.Source, u *user_mode
 			log.Error("UpdateExternalUser failed: %v", err)
 		}
 
+		if err := resetLocale(ctx, u); err != nil {
+			ctx.ServerError("resetLocale", err)
+			return
+		}
+
 		if redirectTo := ctx.GetCookie("redirect_to"); len(redirectTo) > 0 {
 			middleware.DeleteRedirectToCookie(ctx.Resp)
 			ctx.RedirectToFirst(redirectTo)
@@ -1573,6 +1601,11 @@ func handleAccountActivation(ctx *context.Context, user *user_model.User) {
 		log.Error("Error storing session[%s]: %v", ctx.Session.ID(), err)
 	}
 
+	if err := resetLocale(ctx, user); err != nil {
+		ctx.ServerError("resetLocale", err)
+		return
+	}
+
 	ctx.Flash.Success(ctx.Tr("auth.account_activated"))
 	ctx.Redirect(setting.AppSubURL + "/")
 }