diff --git a/abrechenbarkeit.lua b/abrechenbarkeit.lua
index 4eb26a8..c209415 100755
--- a/abrechenbarkeit.lua
+++ b/abrechenbarkeit.lua
@@ -128,9 +128,9 @@ end
 
 local function format_amount(amount, tag, classes)
     local s = format("{+price.amount}", {
-    	sign = amount >= 0 and "+" or "-",
-    	amount = string.format("%.2f", math.abs(amount / 100)),
-    	unit = config.unit or "€"
+        sign = amount >= 0 and "+" or "-",
+        amount = string.format("%.2f", math.abs(amount / 100)),
+        unit = config.unit or "€"
     })
     if tag == nil then return s end
     return format(
@@ -223,13 +223,13 @@ local function respond(status, title, body)
     print("</body></html>")
 end
 
-local function error_box(message)
-    return string.format([[<div class="notif error"><p>Error: %s</p></div>]], escape(message))
+local function error_box(message, params)
+    return string.format([[<div class="notif error"><p>Error: %s</p></div>]], escape(format(message, params)))
 end
 
 local function respond_error(message)
     respond(400, "Error", function()
-        print(error_box(message))
+        print(error_box("{!x}", { x = message }))
     end)
 end
 
@@ -349,25 +349,25 @@ local function r_transaction_post()
             end
         end
         if not exists then
-            return error_box("unknown product")
+            return error_box("{+error.unknown_product}")
         end
     end
     user_src = user_src or "@Potential"
     if amount == nil then
-        return error_box("amount invalid")
+        return error_box("{+error.invalid_amount}")
     end
     if comment == nil or comment:match(matchers_global.comment_opt) == nil then
-        return error_box("comment invalid")
+        return error_box("{+error.invalid_comment}")
     end
     if user_src == nil or user_src:match(matchers_global.user) == nil then
-        return error_box("source user invalid")
+        return error_box("{+error.invalid_user_src}")
     end
     if user_dst == nil or user_dst:match(matchers_global.user) == nil then
-        return error_box("destination user invalid")
+        return error_box("{+error.invalid_user_dst}")
     end
     local log = io.open("log", "a+")
     if log == nil then
-        return error_box("failed to open log")
+        return error_box("{+error.open_log}")
     end
     local time = os.time()
     log:write(string.format("%d,%s,%s,%d,%s,%s,%s\n",
@@ -393,7 +393,8 @@ local function r_user(username)
     return respond(200, string.format("Abrechenbarheit: %s", username), function()
         local is_special = username:sub(1, 1) == "@"
         local username_display = username:gsub("@", "")
-        print(format(is_special and "<h1><i>{!username}</i></h1>" or "<h1>{!username}</h1>", { username = username_display }))
+        print(format(is_special and "<h1><i>{!username}</i></h1>" or "<h1>{!username}</h1>",
+            { username = username_display }))
         local balance = balances()[username]
         local last_txn = last_txns()[username]
         local new_user = balance == nil
@@ -563,7 +564,7 @@ end
 local function r_create_user()
     local username = query.create_user
     if username:match(matchers_global.user) == nil then
-        return respond_error("invalid username " .. username)
+        return respond_error(format("{+error.invalid_user}"))
     end
     return redirect(string.format("/%s", urlencode(username)))
 end
@@ -572,12 +573,12 @@ local function r_products_post()
     local data = form_data()
     local barcode = data.barcode
     if barcode == nil or barcode:match("^[%w_-]*$") == nil then
-        return error_box("barcode invalid")
+        return error_box("{+error.invalid_barcode}")
     end
     if data.delete then
         local new_products = io.open("products.new", "w+")
         if new_products == nil then
-            return error_box("failed to open new products")
+            return error_box("{+error.open_new_products}")
         end
         for a_barcode, price, user, name in read_products() do
             if barcode ~= a_barcode then
@@ -592,17 +593,17 @@ local function r_products_post()
         local name = data.name
         local user = data.user
         if price == nil then
-            return error_box("price invalid")
+            return error_box("{+error.invalid_price}")
         end
         if name == nil or name:match(matchers_global.name) == nil then
-            return error_box("name invalid")
+            return error_box("{+error.invalid_price}")
         end
         if user == nil or user:match(matchers_global.user) == nil then
-            return error_box("user invalid")
+            return error_box("{+error.invalid_user}")
         end
         local products = io.open("products", "a+")
         if products == nil then
-            return error_box("failed to open products")
+            return error_box("{+error.open_products}")
         end
         products:write(string.format("%s,%d,%s,%s\n", barcode, price, user, name))
         products:flush()
@@ -688,7 +689,7 @@ end
 
 local function extract_username()
     if path == nil then
-        return respond_error("no path")
+        return respond_error(format("{+error.no_path}"))
     end
     local username = urldecode(path:sub(2))
     if username == nil or username:match(matchers_global.user) == nil then
@@ -716,7 +717,7 @@ if path == "/" then
 else
     local username = extract_username()
     if username == nil then
-        return respond_error("username invalid")
+        return respond_error(format("{+error.invalid_user}"))
     elseif query.log then
         return r_log(username)
     else
diff --git a/locale/en.ini b/locale/en.ini
index bdaf1d5..6b77621 100644
--- a/locale/en.ini
+++ b/locale/en.ini
@@ -53,3 +53,16 @@ user.form.transaction.success=Transaction successful
 spus=SPUs
 users=Users
 user.special=This is a special user.
+error.unknown_product=Unknown product
+error.invalid_amount=Amount invalid
+error.invalid_comment=Comment invalid
+error.invalid_user_src=Source user invalid
+error.invalid_user_dst=Destination user invalid
+error.invalid_user=Username invalid
+error.open_log=Failed to open log file
+error.invalid_barcode=Barcode invalid
+error.open_new_products=Failed to open new products file
+error.invalid_price=Price invalid
+error.invalid_name=Name invalid
+error.open_products=Failed to open products file
+error.no_path=No path