allow iterables template paths

src/flask/app.py

@@ -158,10 +158,10 @@ class Flask(App):
         Defaults to False.
     :param subdomain_matching: consider the subdomain relative to
         :data:`SERVER_NAME` when matching routes. Defaults to False.
-    :param template_folder: the folder that contains the templates that should
-                            be used by the application.  Defaults to
-                            ``'templates'`` folder in the root path of the
-                            application.
+    :param template_folder: the folder or list of folders that contains the
+                            templates that should be used by the application.
+                            Defaults to ``'templates'`` folder in the root
+                            path of the application.
     :param instance_path: An alternative instance path for the application.
                           By default the folder ``'instance'`` next to the
                           package or module is assumed to be the instance
@@ -231,7 +231,10 @@ class Flask(App):
         static_host: str | None = None,
         host_matching: bool = False,
         subdomain_matching: bool = False,
-        template_folder: str | os.PathLike[str] | None = "templates",
+        template_folder: (
+            str | os.PathLike[str] |
+            t.Sequence[t.Union[str, "os.PathLike[str]"]] | None
+        ) = "templates",
         instance_path: str | None = None,
         instance_relative_config: bool = False,
         root_path: str | None = None,

src/flask/blueprints.py

@@ -22,7 +22,10 @@ class Blueprint(SansioBlueprint):
         import_name: str,
         static_folder: str | os.PathLike[str] | None = None,
         static_url_path: str | None = None,
-        template_folder: str | os.PathLike[str] | None = None,
+        template_folder: (
+            str | os.PathLike[str] | None |
+            t.Sequence[t.Union[str, "os.PathLike[str]"]] | None
+        )= None,
         url_prefix: str | None = None,
         subdomain: str | None = None,
         url_defaults: dict[str, t.Any] | None = None,

src/flask/sansio/app.py

@@ -136,10 +136,10 @@ class App(Scaffold):
         Defaults to False.
     :param subdomain_matching: consider the subdomain relative to
         :data:`SERVER_NAME` when matching routes. Defaults to False.
-    :param template_folder: the folder that contains the templates that should
-                            be used by the application.  Defaults to
-                            ``'templates'`` folder in the root path of the
-                            application.
+    :param template_folder: the folder or list of folders that contains the
+                            templates that should be used by the application.
+                            Defaults to ``'templates'`` folder in the root
+                            path of the application.
     :param instance_path: An alternative instance path for the application.
                           By default the folder ``'instance'`` next to the
                           package or module is assumed to be the instance
@@ -287,7 +287,10 @@ class App(Scaffold):
         static_host: str | None = None,
         host_matching: bool = False,
         subdomain_matching: bool = False,
-        template_folder: str | os.PathLike[str] | None = "templates",
+        template_folder: (
+            str | os.PathLike[str] |
+            t.Sequence[t.Union[str, "os.PathLike[str]"]] | None
+        ) = "templates",
         instance_path: str | None = None,
         instance_relative_config: bool = False,
         root_path: str | None = None,

src/flask/sansio/blueprints.py

@@ -145,9 +145,10 @@ class Blueprint(Scaffold):
         Defaults to ``static_folder``. If the blueprint does not have
         a ``url_prefix``, the app's static route will take precedence,
         and the blueprint's static files won't be accessible.
-    :param template_folder: A folder with templates that should be added
-        to the app's template search path. The path is relative to the
-        blueprint's root path. Blueprint templates are disabled by
+    :param template_folder: A folder or list of folders with templates
+        that should be added to the app's template search path.
+        The path is relative to the blueprint's root path is absolute
+        paths is not presented. Blueprint templates are disabled by
         default. Blueprint templates have a lower precedence than those
         in the app's templates folder.
     :param url_prefix: A path to prepend to all of the blueprint's URLs,
@@ -177,7 +178,10 @@ class Blueprint(Scaffold):
         import_name: str,
         static_folder: str | os.PathLike[str] | None = None,
         static_url_path: str | None = None,
-        template_folder: str | os.PathLike[str] | None = None,
+        template_folder: (
+            str | os.PathLike[str] |
+            t.Sequence[t.Union[str, "os.PathLike[str]"]] | None
+        ) = None,
         url_prefix: str | None = None,
         subdomain: str | None = None,
         url_defaults: dict[str, t.Any] | None = None,

src/flask/sansio/scaffold.py

@@ -6,6 +6,7 @@ import pathlib
 import sys
 import typing as t
 from collections import defaultdict
+from collections.abc import Sequence
 from functools import update_wrapper
 
 from jinja2 import BaseLoader
@@ -58,7 +59,7 @@ class Scaffold:
     :param static_folder: Path to a folder of static files to serve.
         If this is set, a static route will be added.
     :param static_url_path: URL prefix for the static route.
-    :param template_folder: Path to a folder containing template files.
+    :param template_folder: Path or list of paths to a folder containing template files.
         for rendering. If this is set, a Jinja loader will be added.
     :param root_path: The path that static, template, and resource files
         are relative to. Typically not set, it is discovered based on
@@ -77,7 +78,10 @@ class Scaffold:
         import_name: str,
         static_folder: str | os.PathLike[str] | None = None,
         static_url_path: str | None = None,
-        template_folder: str | os.PathLike[str] | None = None,
+        template_folder: (
+            str | os.PathLike[str] |
+            t.Sequence[t.Union[str, "os.PathLike[str]"]] | None
+        ) = None,
         root_path: str | None = None,
     ):
         #: The name of the package or module that this object belongs
@@ -276,10 +280,18 @@ class Scaffold:
 
         .. versionadded:: 0.5
         """
-        if self.template_folder is not None:
-            return FileSystemLoader(os.path.join(self.root_path, self.template_folder))
-        else:
+
+        if self.template_folder is None:
             return None
+        if isinstance(self.template_folder, str):
+            return FileSystemLoader(
+                os.path.join(self.root_path, self.template_folder)
+            )
+        return FileSystemLoader([
+            folder if isinstance(folder, os.PathLike)
+            else os.path.join(self.root_path, folder)
+            for folder in self.template_folder
+        ])
 
     def _method_route(
         self,