Index: app/models/user.rb
===================================================================
--- app/models/user.rb	(revision 15144)
+++ app/models/user.rb	(working copy)
@@ -106,7 +106,7 @@
   validates_presence_of :login, :firstname, :lastname, :if => Proc.new { |user| !user.is_a?(AnonymousUser) }
   validates_uniqueness_of :login, :if => Proc.new { |user| user.login_changed? && user.login.present? }, :case_sensitive => false
   # Login must contain letters, numbers, underscores only
-  validates_format_of :login, :with => /\A[a-z0-9_\-@\.]*\z/i
+  validates_format_of :login, :with => /\A[[:alnum:]_\-@\.]*\z/i
   validates_length_of :login, :maximum => LOGIN_LENGTH_LIMIT
   validates_length_of :firstname, :lastname, :maximum => 30
   validates_inclusion_of :mail_notification, :in => MAIL_NOTIFICATION_OPTIONS.collect(&:first), :allow_blank => true
Index: test/unit/user_test.rb
===================================================================
--- test/unit/user_test.rb	(revision 15144)
+++ test/unit/user_test.rb	(working copy)
@@ -105,6 +105,13 @@
     assert user.save
   end
 
+  def test_login_with_umlauts
+    user = User.new(:firstname => "new", :lastname => "user", :mail => "newuser@somenet.foo")
+    user.login = "Jörg"
+    assert user.valid?
+    assert user.save
+  end
+
   def test_generate_password_should_respect_minimum_password_length
     with_settings :password_min_length => 15 do
       user = User.generate!(:generate_password => true)