diff --git a/changelogs/fragments/6774-locale-gen-fix.yml b/changelogs/fragments/6774-locale-gen-fix.yml
new file mode 100644
index 0000000000..fc71022f06
--- /dev/null
+++ b/changelogs/fragments/6774-locale-gen-fix.yml
@@ -0,0 +1,2 @@
+bugfixes:
+  - locale_gen - now works for locales without the underscore character such as ``C.UTF-8`` (https://github.com/ansible-collections/community.general/pull/6774, https://github.com/ansible-collections/community.general/issues/5142, https://github.com/ansible-collections/community.general/issues/4305).
diff --git a/plugins/modules/locale_gen.py b/plugins/modules/locale_gen.py
index fccdf977a4..36c304ea69 100644
--- a/plugins/modules/locale_gen.py
+++ b/plugins/modules/locale_gen.py
@@ -35,6 +35,8 @@ options:
             - Whether the locale shall be present.
         choices: [ absent, present ]
         default: present
+notes:
+    - This module does not support RHEL-based systems.
 '''
 
 EXAMPLES = '''
@@ -74,11 +76,10 @@ def is_available(name, ubuntuMode):
     checking either :
     * if the locale is present in /etc/locales.gen
     * or if the locale is present in /usr/share/i18n/SUPPORTED"""
+    __regexp = r'^#?\s*(?P<locale>\S+[\._\S]*) (?P<charset>\S+)\s*$'
     if ubuntuMode:
-        __regexp = r'^(?P<locale>\S+_\S+) (?P<charset>\S+)\s*$'
         __locales_available = '/usr/share/i18n/SUPPORTED'
     else:
-        __regexp = r'^#{0,1}\s*(?P<locale>\S+_\S+) (?P<charset>\S+)\s*$'
         __locales_available = '/etc/locale.gen'
 
     re_compiled = re.compile(__regexp)
@@ -88,7 +89,8 @@ def is_available(name, ubuntuMode):
         if result and result.group('locale') == name:
             return True
     fd.close()
-    return False
+    # locale may be installed but not listed in the file, for example C.UTF-8 in some systems
+    return is_present(name)
 
 
 def is_present(name):
@@ -106,20 +108,6 @@ def fix_case(name):
     return name
 
 
-def replace_line(existing_line, new_line):
-    """Replaces lines in /etc/locale.gen"""
-    try:
-        f = open("/etc/locale.gen", "r")
-        lines = [line.replace(existing_line, new_line) for line in f]
-    finally:
-        f.close()
-    try:
-        f = open("/etc/locale.gen", "w")
-        f.write("".join(lines))
-    finally:
-        f.close()
-
-
 def set_locale(name, enabled=True):
     """ Sets the state of the locale. Defaults to enabled. """
     search_string = r'#{0,1}\s*%s (?P<charset>.+)' % name
@@ -209,7 +197,7 @@ def main():
             # We found the common way to manage locales.
             ubuntuMode = False
         else:
-            module.fail_json(msg="/etc/locale.gen and /var/lib/locales/supported.d/local are missing. Is the package \"locales\" installed?")
+            module.fail_json(msg="/etc/locale.gen and /var/lib/locales/supported.d/local are missing. Is the package 'locales' installed?")
     else:
         # Ubuntu created its own system to manage locales.
         ubuntuMode = True
diff --git a/tests/integration/targets/locale_gen/aliases b/tests/integration/targets/locale_gen/aliases
index f7f4063f6c..a5d3e27f9e 100644
--- a/tests/integration/targets/locale_gen/aliases
+++ b/tests/integration/targets/locale_gen/aliases
@@ -6,3 +6,5 @@ azp/posix/3
 destructive
 needs/root
 skip/aix
+skip/freebsd
+skip/macos
diff --git a/tests/integration/targets/locale_gen/tasks/basic.yml b/tests/integration/targets/locale_gen/tasks/basic.yml
new file mode 100644
index 0000000000..8718e0be8b
--- /dev/null
+++ b/tests/integration/targets/locale_gen/tasks/basic.yml
@@ -0,0 +1,102 @@
+---
+# Copyright (c) Ansible Project
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+- name: Is the locale we're going to test against installed? {{ locale_basic.localegen }}
+  command: locale -a
+  register: initial_state
+  ignore_errors: true
+
+- name: Make sure the locale is not installed {{ locale_basic.localegen }}
+  locale_gen:
+    name: "{{ locale_basic.localegen }}"
+    state: absent
+
+- name: Is the locale present? {{ locale_basic.localegen }}
+  command: locale -a
+  register: cleaned
+  ignore_errors: true
+
+- name: Make sure the locale is not present {{ locale_basic.localegen }}
+  assert:
+    that:
+      - locale_basic.skip_removal or locale_basic.locales | intersect(cleaned.stdout_lines) == []
+
+- name: Install the locale {{ locale_basic.localegen }}
+  locale_gen:
+    name: "{{ locale_basic.localegen }}"
+    state: present
+  register: output_present
+
+- name: Is the locale present? {{ locale_basic.localegen }}
+  command: locale -a
+  register: post_check_output_present
+  ignore_errors: true
+
+- name: Make sure the locale is present and we say we installed it {{ locale_basic.localegen }}
+  assert:
+    that:
+      - locale_basic.locales | intersect(post_check_output_present.stdout_lines) != []
+      - locale_basic.skip_removal or output_present is changed
+
+- name: Install the locale a second time {{ locale_basic.localegen }}
+  locale_gen:
+    name: "{{ locale_basic.localegen }}"
+    state: present
+  register: output_present_idempotent
+
+- name: Is the locale present? {{ locale_basic.localegen }}
+  command: locale -a
+  register: post_check_output_present_idempotent
+  ignore_errors: true
+
+- name: Make sure the locale is present and we reported no change {{ locale_basic.localegen }}
+  assert:
+    that:
+      - locale_basic.locales | intersect(post_check_output_present_idempotent.stdout_lines) != []
+      - output_present_idempotent is not changed
+
+- name: Removals
+  when: locale_basic.skip_removal is false
+  block:
+    - name: Remove the locale {{ locale_basic.localegen }}
+      locale_gen:
+        name: "{{ locale_basic.localegen }}"
+        state: absent
+      register: output_absent
+
+    - name: Is the locale present? {{ locale_basic.localegen }}
+      command: locale -a
+      register: post_check_output_absent
+      ignore_errors: true
+
+    - name: Make sure the locale is absent and we reported a change {{ locale_basic.localegen }}
+      assert:
+        that:
+          - locale_basic.locales | intersect(post_check_output_absent.stdout_lines) == []
+          - output_absent is changed
+
+    - name: Remove the locale a second time {{ locale_basic.localegen }}
+      locale_gen:
+        name: "{{ locale_basic.localegen }}"
+        state: absent
+      register: output_absent_idempotent
+
+    - name: Is the locale present? {{ locale_basic.localegen }}
+      command: locale -a
+      register: post_check_output_absent_idempotent
+      ignore_errors: true
+
+    - name: Make sure the locale is absent and we reported no change {{ locale_basic.localegen }}
+      assert:
+        that:
+          - locale_basic.locales | intersect(post_check_output_absent_idempotent.stdout_lines) == []
+          - output_absent_idempotent is not changed
+
+# Cleanup
+- name: Reinstall the locale we tested against if it was initially installed {{ locale_basic.localegen }}
+  locale_gen:
+    name: "{{ locale_basic.localegen }}"
+    state: present
+  when: locale_basic.locales | intersect(initial_state.stdout_lines) != []
diff --git a/tests/integration/targets/locale_gen/tasks/locale_gen.yml b/tests/integration/targets/locale_gen/tasks/locale_gen.yml
deleted file mode 100644
index c6bdcc046b..0000000000
--- a/tests/integration/targets/locale_gen/tasks/locale_gen.yml
+++ /dev/null
@@ -1,99 +0,0 @@
----
-# Copyright (c) Ansible Project
-# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
-# SPDX-License-Identifier: GPL-3.0-or-later
-
-- name: Is the locale we're going to test against installed?
-  shell: locale -a | grep pt_BR
-  register: initial_state
-  ignore_errors: true
-
-- name: Make sure the locale is not installed
-  locale_gen:
-    name: pt_BR
-    state: absent
-
-- name: Is the locale present?
-  shell: locale -a | grep pt_BR
-  register: cleaned
-  ignore_errors: true
-
-- name: Make sure the locale is not present
-  assert:
-    that:
-      - "cleaned.rc == 1"
-
-- name: Install the locale
-  locale_gen:
-    name: pt_BR
-    state: present
-  register: output
-
-- name: Is the locale present?
-  shell: locale -a | grep pt_BR
-  register: post_check_output
-  ignore_errors: true
-
-- name: Make sure the locale is present and we say we installed it
-  assert:
-    that:
-      - "post_check_output.rc == 0"
-      - "output.changed"
-
-- name: Install the locale a second time
-  locale_gen:
-    name: pt_BR
-    state: present
-  register: output
-
-- name: Is the locale present?
-  shell: locale -a | grep pt_BR
-  register: post_check_output
-  ignore_errors: true
-
-- name: Make sure the locale is present and we reported no change
-  assert:
-    that:
-      - "post_check_output.rc == 0"
-      - "not output.changed"
-
-- name: Remove the locale
-  locale_gen:
-    name: pt_BR
-    state: absent
-  register: output
-
-- name: Is the locale present?
-  shell: locale -a | grep pt_BR
-  register: post_check_output
-  ignore_errors: true
-
-- name: Make sure the locale is absent and we reported a change
-  assert:
-    that:
-      - "post_check_output.rc == 1"
-      - "output.changed"
-
-- name: Remove the locale a second time
-  locale_gen:
-    name: pt_BR
-    state: absent
-  register: output
-
-- name: Is the locale present?
-  shell: locale -a | grep pt_BR
-  register: post_check_output
-  ignore_errors: true
-
-- name: Make sure the locale is absent and we reported no change
-  assert:
-    that:
-      - "post_check_output.rc == 1"
-      - "not output.changed"
-
-# Cleanup
-- name: Reinstall the locale we tested against if it was initially installed
-  locale_gen:
-    name: pt_BR
-    state: present
-  when: initial_state.rc == 0
diff --git a/tests/integration/targets/locale_gen/tasks/main.yml b/tests/integration/targets/locale_gen/tasks/main.yml
index de3e673beb..2d9dfcee04 100644
--- a/tests/integration/targets/locale_gen/tasks/main.yml
+++ b/tests/integration/targets/locale_gen/tasks/main.yml
@@ -8,5 +8,11 @@
 # GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
 # SPDX-License-Identifier: GPL-3.0-or-later
 
-- include_tasks: 'locale_gen.yml'
-  when: ansible_distribution in ('Ubuntu', 'Debian')
+- name: Bail out if not supported
+  ansible.builtin.meta: end_play
+  when: ansible_distribution not in ('Ubuntu', 'Debian')
+
+- include_tasks: basic.yml
+  loop: "{{ locale_list_basic }}"
+  loop_control:
+    loop_var: locale_basic
diff --git a/tests/integration/targets/locale_gen/vars/main.yml b/tests/integration/targets/locale_gen/vars/main.yml
new file mode 100644
index 0000000000..44327ddd31
--- /dev/null
+++ b/tests/integration/targets/locale_gen/vars/main.yml
@@ -0,0 +1,17 @@
+---
+# Copyright (c) Ansible Project
+# GNU General Public License v3.0+ (see LICENSES/GPL-3.0-or-later.txt or https://www.gnu.org/licenses/gpl-3.0.txt)
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+# locale_basic: pt_BR
+
+locale_list_basic:
+  - localegen: pt_BR
+    locales: [pt_BR]
+    skip_removal: false
+  - localegen: C.UTF-8
+    locales: [C.utf8, C.UTF-8]
+    skip_removal: true
+  - localegen: eo
+    locales: [eo]
+    skip_removal: false