diff --git a/README.md b/README.md
index de72aa8..72be632 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # python Captive Portal
 
-### Installation
+## Installation
 
 Either clone repository (and install dependencies either through distribution or as virtualenv with `./setup-venv.sh`) or install as package.
 
@@ -8,3 +8,12 @@ Either clone repository (and install dependencies either through distribution or
 
     pipx install https://github.tik.uni-stuttgart.de/NKS/python-capport
 
+In production put a reverse proxy in front of the local web ui (on 127.0.0.1:8000), and handle `/static` path either to `src/capport/api/static/` or your customized version of static files.
+
+## Customization
+
+Create `custom/templates` and put customized templates (from `src/capport/api/templates`) there.
+
+Create `i18n/<langcode>` folders to put localized templates into.
+
+Requests with a `setlang=<langcode>` query parameter will set the language and try to store the choice in a session cookie.
diff --git a/src/capport/api/app.py b/src/capport/api/app.py
index b9e144e..70ab89e 100644
--- a/src/capport/api/app.py
+++ b/src/capport/api/app.py
@@ -5,4 +5,5 @@ app = MyQuartApp(__name__)
 
 
 __import__('capport.api.setup')
+__import__('capport.api.lang')
 __import__('capport.api.views')
diff --git a/src/capport/api/app_cls.py b/src/capport/api/app_cls.py
index f7e8220..e33e2b5 100644
--- a/src/capport/api/app_cls.py
+++ b/src/capport/api/app_cls.py
@@ -18,6 +18,26 @@ class DispatchingJinjaLoader(quart.templating.DispatchingJinjaLoader):
     def __init__(self, app: MyQuartApp) -> None:
         super().__init__(app)
 
+    def get_source(
+        self, environment: jinja2.Environment, template: str
+    ) -> typing.Tuple[str, typing.Optional[str], typing.Optional[typing.Callable[[], bool]]]:
+        """Returns the template source from the environment.
+
+        This considers the loaders on the :attr:`app` and blueprints.
+        """
+        langs: typing.List[str] = quart.g.langs
+        for loader in self._loaders():
+            for lang in langs:
+                try:
+                    return loader.get_source(environment, os.path.join('i18n', lang, template))
+                except jinja2.TemplateNotFound:
+                    continue
+            try:
+                return loader.get_source(environment, template)
+            except jinja2.TemplateNotFound:
+                continue
+        raise jinja2.TemplateNotFound(template)
+
     def _loaders(self) -> typing.Generator[jinja2.BaseLoader, None, None]:
         if self.app.custom_loader:
             yield self.app.custom_loader
diff --git a/src/capport/api/lang.py b/src/capport/api/lang.py
new file mode 100644
index 0000000..0789b6c
--- /dev/null
+++ b/src/capport/api/lang.py
@@ -0,0 +1,67 @@
+from __future__ import annotations
+
+import re
+import typing
+import quart
+
+from .app import app
+
+_VALID_LANGUAGE_NAMES = re.compile(r'^[-a-z0-9_]+$')
+
+
+def parse_accept_language(value: str) -> typing.List[str]:
+    value = value.strip()
+    if not value or value == '*':
+        return []
+    tuples = []
+    for entry in value.split(','):
+        attrs = entry.split(';')
+        name = attrs.pop(0).strip().lower()
+        q = 1.0
+        for attr in attrs:
+            if not '=' in attr: continue
+            key, value = attr.split('=', maxsplit=1)
+            if key.strip().lower() == 'q':
+                try:
+                    q = float(value.strip())
+                except ValueError:
+                    q = 0.0
+        if q >= 0.0:
+            tuples.append((q, name))
+    tuples.sort()
+    have = set()
+    result = []
+    for (_q, name) in tuples:
+        if name in have: continue
+        if name == '*': break
+        have.add(name)
+        if _VALID_LANGUAGE_NAMES.match(name):
+            result.append(name)
+        short_name = name.split('-', maxsplit=1)[0].split('_', maxsplit=1)[0]
+        if not short_name or short_name in have: continue
+        have.add(short_name)
+        result.append(short_name)
+    return result
+
+
+@app.before_request
+def detect_language():
+    g = quart.g
+    r = quart.request
+    s = quart.session
+    lang = r.args.get('setlang')
+    if lang:
+        lang = lang.strip().lower()
+        if lang and _VALID_LANGUAGE_NAMES.match(lang):
+            s = quart.session
+            s['lang'] = lang
+            g.langs = [lang]
+            return
+    lang = s.get('lang')
+    if lang:
+        lang = lang.strip().lower()
+        if lang and _VALID_LANGUAGE_NAMES.match(lang):
+            g.langs = [lang]
+            return
+    acc_lang = ','.join(r.headers.get_all('Accept-Language'))
+    g.langs = parse_accept_language(acc_lang)