diff --git a/release/scripts/modules/bl_i18n_utils/bl_extract_messages.py b/release/scripts/modules/bl_i18n_utils/bl_extract_messages.py
index 18c7b736ea5..7876a443035 100644
--- a/release/scripts/modules/bl_i18n_utils/bl_extract_messages.py
+++ b/release/scripts/modules/bl_i18n_utils/bl_extract_messages.py
@@ -408,6 +408,14 @@ def dump_py_messages_from_files(msgs, reports, files, settings):
 
     bpy_struct = bpy.types.ID.__base__
 
+    root_paths = tuple(bpy.utils.resource_path(t) for t in ('USER', 'LOCAL', 'SYSTEM'))
+    def make_rel(path):
+        for rp in root_paths:
+            if path.startswith(rp):
+                return os.path.relpath(path, rp)
+        # Use binary's dir as fallback...
+        return os.path.relpath(path, os.path.dirname(bpy.app.binary_path))
+
     # Helper function
     def extract_strings_ex(node, is_split=False):
         """
@@ -559,7 +567,7 @@ def dump_py_messages_from_files(msgs, reports, files, settings):
         with open(fp, 'r', encoding="utf8") as filedata:
             root_node = ast.parse(filedata.read(), fp, 'exec')
 
-        fp_rel = os.path.relpath(fp, settings.SOURCE_DIR)
+        fp_rel = make_rel(fp)
 
         for node in ast.walk(root_node):
             if type(node) == ast.Call:
@@ -623,19 +631,22 @@ def dump_py_messages_from_files(msgs, reports, files, settings):
                             reports["py_messages"].append((msgctxt, estr, msgsrc))
 
 
-def dump_py_messages(msgs, reports, addons, settings):
+def dump_py_messages(msgs, reports, addons, settings, addons_only=False):
     def _get_files(path):
+        if not os.path.exists(path):
+            return []
         if os.path.isdir(path):
-            # XXX use walk instead of listdir?
-            return [os.path.join(path, fn) for fn in sorted(os.listdir(path))
-                                              if not fn.startswith("_") and fn.endswith(".py")]
+            return [os.path.join(dpath, fn) for dpath, _, fnames in os.walk(path) for fn in fnames
+                                            if not fn.startswith("_") and fn.endswith(".py")]
         return [path]
 
     files = []
-    for path in settings.CUSTOM_PY_UI_FILES:
-        files += _get_files(path)
+    if not addons_only:
+        for path in settings.CUSTOM_PY_UI_FILES:
+            for root in (bpy.utils.resource_path(t) for t in ('USER', 'LOCAL', 'SYSTEM')):
+                files += _get_files(os.path.join(root, path))
 
-    # Add all addons we support in main translation file!
+    # Add all given addons.
     for mod in addons:
         fn = mod.__file__
         if os.path.basename(fn) == "__init__.py":
@@ -643,7 +654,7 @@ def dump_py_messages(msgs, reports, addons, settings):
         else:
             files.append(fn)
 
-    dump_py_messages_from_files(msgs, reports, files, settings)
+    dump_py_messages_from_files(msgs, reports, sorted(files), settings)
 
 
 ##### C source code #####
@@ -855,7 +866,7 @@ def dump_addon_messages(module_name, messages_formats, do_checks, settings):
 
     # get strings from UI layout definitions text="..." args
     reports["check_ctxt"] = check_ctxt
-    dump_messages_pytext(msgs, reports, addons, settings)
+    dump_messages_pytext(msgs, reports, addons, settings, addons_only=True)
 
     print_info(reports, pot)
 
diff --git a/release/scripts/modules/bl_i18n_utils/settings.py b/release/scripts/modules/bl_i18n_utils/settings.py
index 31eac77b358..48761a35c99 100644
--- a/release/scripts/modules/bl_i18n_utils/settings.py
+++ b/release/scripts/modules/bl_i18n_utils/settings.py
@@ -384,11 +384,10 @@ MO_PATH_TEMPLATE_RELATIVE = os.path.join(MO_PATH_ROOT_RELATIVE, "{}", "LC_MESSAG
 # Mo file name.
 MO_FILE_NAME = DOMAIN + ".mo"
 
-# Where to search for py files that may contain ui strings (relative to SOURCE_DIR).
-REL_CUSTOM_PY_UI_FILES = [
-    os.path.join("release", "scripts", "startup", "bl_ui"),
-    os.path.join("intern", "cycles", "blender", "addon", "ui.py"),
-    os.path.join("release", "scripts", "modules", "rna_prop_ui.py"),
+# Where to search for py files that may contain ui strings (relative to one of the 'resource_path' of Blender).
+CUSTOM_PY_UI_FILES = [
+    os.path.join("scripts", "startup", "bl_ui"),
+    os.path.join("scripts", "modules", "rna_prop_ui.py"),
 ]
 
 # An optional text file listing files to force include/exclude from py_xgettext process.
@@ -503,7 +502,6 @@ class I18nSettings:
     FILE_NAME_POT = property(*(_gen_get_set_path("I18N_DIR", "REL_FILE_NAME_POT")))
     MO_PATH_ROOT = property(*(_gen_get_set_path("I18N_DIR", "REL_MO_PATH_ROOT")))
     MO_PATH_TEMPLATE = property(*(_gen_get_set_path("I18N_DIR", "REL_MO_PATH_TEMPLATE")))
-    CUSTOM_PY_UI_FILES = property(*(_gen_get_set_paths("SOURCE_DIR", "REL_CUSTOM_PY_UI_FILES")))
 
     def _get_py_sys_paths(self):
         return self.INTERN_PY_SYS_PATHS