diff --git a/fgs/__main__.py b/fgs/__main__.py
index 501fed3730199097468b42f9b159f3e318f53267..54bca9a1cd983cfc77afde2cf89964afc260af99 100644
--- a/fgs/__main__.py
+++ b/fgs/__main__.py
@@ -5,6 +5,7 @@ import os
 import sys
 
 
+import common
 import datatypes
 import reader
 import generator
@@ -19,11 +20,13 @@ def main():
     print("Hello World")
     config = {}
     with open('../config.json') as f:
-        config.update(json.loads(f.read()))
+        config = common.combine(config, json.loads(f.read()))
     with open('../lang.json') as f:
-        config['lang'] = json.loads(f.read())
+        if 'lang' not in config:
+            config['lang'] = {}
+        config['lang'] = common.combine(config['lang'], json.loads(f.read()))
     with open(CONTENT_DIR + '/config.json') as f:
-        config.update(json.loads(f.read()))
+        config = common.combine(config, json.loads(f.read()))
     print(config)
 
     factories = {}
@@ -62,6 +65,7 @@ def main():
 
 
 
+
 def read_static_dir(directory, static_files, subpath = []):
     print("static_dir: " + directory);
     for filename in os.listdir(directory):
diff --git a/fgs/common.py b/fgs/common.py
new file mode 100644
index 0000000000000000000000000000000000000000..007d969162aca88a5837460e1ee02bcce1679f3e
--- /dev/null
+++ b/fgs/common.py
@@ -0,0 +1,14 @@
+
+def combine(old, new):
+    if type(old) != type(new):
+        raise Exception("Cannot combine different types: ", type(old), type(new), old, new)
+    if isinstance(old, dict):
+        res = old.copy()
+        for key, value in new.items():
+            if key in res:
+                res[key] = combine(res[key], value)
+            else:
+                res[key] = value
+        return res
+    else:
+        return new
diff --git a/fgs/datatypes.py b/fgs/datatypes.py
index 01c4631d04b679bed43b9f2a5fcea874083893a0..938f1e6610ba738e3bef8636cf46ef8659c4ce01 100644
--- a/fgs/datatypes.py
+++ b/fgs/datatypes.py
@@ -1,6 +1,8 @@
 import datetime
 from dateutil import parser as dtparser
 
+import common
+
 class DictConverter:
 
     def __init__(self, factories):
@@ -106,8 +108,7 @@ class Page:
         if self.lang == deflang:
             return self._metadata
         defpage = self._factories['page'].get(self.slug, deflang)
-        res = defpage.metadata.copy()
-        res.update(self._metadata)
+        res = common.combine(defpage.metadata, self._metadata)
         return res
     metadata = property(get_metadata, None, None)
 
diff --git a/fgs/writer.py b/fgs/writer.py
index ebeb32c980a23c9c0a830cdc1e30490162757ff5..3b18f31412c25fd996868ae40b7a8054a17fa3ff 100644
--- a/fgs/writer.py
+++ b/fgs/writer.py
@@ -2,6 +2,8 @@ from jinja2 import Environment, FileSystemLoader, StrictUndefined
 
 import os
 
+import common
+
 class Writer:
 
     def __init__(self, config, context, output_dir, theme_dir):
@@ -35,7 +37,7 @@ class Writer:
 
         # render template
         context = {}
-        context.update(self.context)
+        context = common.combine(context, self.context)
         context["config"] = localized_config
         context["theme"] = localized_config['theme']
         context["template"] = template
@@ -43,7 +45,7 @@ class Writer:
         context["l"] = lang # current language
         context["path"] = path
         context["siteurl"] = siteurl
-        context.update(extra_context)
+        context = common.combine(context, extra_context)
         #print("template: ", template)
         #print("path: ", path)
         #print("lang: ", lang)