diff --git a/app/models/user.rb b/app/models/user.rb
index 51cce45acae2..d7cd19c38e7b 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -129,7 +129,7 @@ def self.blocked_condition(blocked)
   validates :login, uniqueness: { if: Proc.new { |user| user.login.present? }, case_sensitive: false }
   validates :mail, uniqueness: { allow_blank: true, case_sensitive: false }
   # Login must contain letters, numbers, underscores only
-  validates :login, format: { with: /\A[a-z0-9_\-@.+ ]*\z/i }
+  validates :login, format: { with: /\A[\p{L}0-9_\-@.+ ]*\z/i }
   validates :login, length: { maximum: 256 }
 
   validates :firstname, :lastname, length: { maximum: 256 }
diff --git a/docs/development/ldap/README.md b/docs/development/ldap/README.md
new file mode 100644
index 000000000000..2f3a9dfb3fcd
--- /dev/null
+++ b/docs/development/ldap/README.md
@@ -0,0 +1,31 @@
+---
+sidebar_navigation:
+  title: LDAP development setup
+  priority: 920
+---
+
+# Set up a development LDAP server
+
+**Note:** This guide is targeted only at development with OpenProject. For the LDAP configuration guide, please see this [here](../../system-admin-guide/authentication/ldap-authentication/)
+
+
+OpenProject comes with a built-in LDAP server for development purposes. This server uses [ladle gem](https://github.com/NUBIC/ladle)
+to run an underlying apacheDS server.
+
+This guide will show you how to set it up in your development instance.
+
+## Prerequisites
+
+- A local java/JRE environment installed (openjdk, java installed via homebrew, etc.)
+- A development setup of OpenProject (or any other configurable installation)
+
+## Running the LDAP server
+
+You only need to run this rake task to start the server:
+
+```bash
+./bin/rails ldap_groups:development:ldap_server
+```
+
+It will both output the different users and groups, as well as connection details. Starting this task will ensure
+an LDAP connection is created or updated to make sure you can use it right away.
diff --git a/modules/ldap_groups/lib/tasks/ldap_groups.rake b/modules/ldap_groups/lib/tasks/ldap_groups.rake
index ff24331508a8..e23f4deb538c 100644
--- a/modules/ldap_groups/lib/tasks/ldap_groups.rake
+++ b/modules/ldap_groups/lib/tasks/ldap_groups.rake
@@ -128,6 +128,7 @@ namespace :ldap_groups do
         uid=aa729,ou=people,dc=example,dc=com (Password: smada)
         uid=bb459,ou=people,dc=example,dc=com (Password: niwdlab)
         uid=cc414,ou=people,dc=example,dc=com (Password: retneprac)
+        uid=bölle,ou=people,dc=example,dc=com (Password: bólle)
 
         --------------------------------------------------------
 
diff --git a/spec/fixtures/ldap/users.ldif b/spec/fixtures/ldap/users.ldif
index e369e7cd773f..1daaeed36865 100644
--- a/spec/fixtures/ldap/users.ldif
+++ b/spec/fixtures/ldap/users.ldif
@@ -182,3 +182,17 @@ mail: xara@example.org
 uid: xx396
 userpassword:: e1NIQX1ZYzJFbjJSL3NiZGpsRU9pdGtMbGt3WTRqQVk9
 
+dn: uid=bölle,ou=people,dc=example,dc=com
+objectClass: inetOrgPerson
+objectClass: simulatedMicrosoftSecurityPrincipal
+objectClass: organizationalPerson
+objectClass: person
+objectClass: top
+cn: Bölle Büllendorf
+sn: Büllendorf
+givenName: Bölle
+mail: boelle@example.org
+uid: bölle
+samAccountName: bölle
+# Password is "bólle"
+userpassword:: e1NIQX1rNDBGWHRYQ3RFL3l2cENhblRpQmZ2cE1ON1k9Cg==
diff --git a/spec/models/user_spec.rb b/spec/models/user_spec.rb
index 9bbcb97d49f5..121b8bdce4fc 100644
--- a/spec/models/user_spec.rb
+++ b/spec/models/user_spec.rb
@@ -143,6 +143,18 @@
         end
       end
 
+      context 'with other letter char classes' do
+        let(:login) { "célîneüberölig" }
+
+        it 'is valid' do
+          expect(user).to be_valid
+        end
+
+        it 'may be stored in the database' do
+          expect(user.save).to be_truthy
+        end
+      end
+
       context "with tabs" do
         let(:login) { 'ab\tc' }
 
@@ -172,7 +184,7 @@
       end
 
       context "with combination thereof" do
-        let(:login) { "the+boss-is@the_house." }
+        let(:login) { "the+boss-is-über@the_house." }
 
         it "is valid" do
           expect(user).to be_valid
diff --git a/spec/requests/auth/ldap_sso_spec.rb b/spec/requests/auth/ldap_sso_spec.rb
index 5d2858a013a6..d1367a9fc0c9 100644
--- a/spec/requests/auth/ldap_sso_spec.rb
+++ b/spec/requests/auth/ldap_sso_spec.rb
@@ -58,6 +58,23 @@
       expect(subject).to redirect_to "/?first_time_user=true"
     end
 
+    context 'with a user that has umlauts in their name' do
+      let(:username) { 'bölle' }
+      let(:password) { 'bólle' }
+
+      it 'creates a user with umlauts on the fly' do
+        expect(User.find_by(login: 'bölle')).to be_nil
+
+        expect { subject }.to change(User.not_builtin.active, :count).by(1)
+
+        user = User.find_by(login: 'bölle')
+        expect(user).to be_present
+        expect(user).to be_active
+        expect(session[:user_id]).to eq user.id
+        expect(subject).to redirect_to '/?first_time_user=true'
+      end
+    end
+
     context "when not all attributes present" do
       let(:attr_mail) { nil }