diff --git a/README.md b/README.md
index e78cd7b..d40bade 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,28 @@
 This is the development project for the Curriculum Vitae of Axel Herrmann.  
 See the newest deployed version at https://axherrm.github.io/CV/
 
+## How to fill the template
+
+All data displayed on the CV is stored in [src/data].  
+Use the following steps to insert your own data:
+> ### 1. [languages.json]
+> 
+> This file contains a definition of the languages that can be used in the CV as well as a definition of section headings etc. for each language.
+> if all languages you want to use are defined you only need to adjust the languages array.
+> 
+> | Field                 | Description                                                                                 |
+> |-----------------------|---------------------------------------------------------------------------------------------|
+> | `languages`           | Array of IDs of all available languages                                                     |
+> | `defaultLanguage`     | ID of language that should be used when no locale could be determined                       |
+> | `${IDs of languages}` | Each of the above listed languages needs a `LanguagePack` object like defined in [model.ts] |
+> 
+> ### 2. Other JSON files
+> 
+> The other JSON in [src/data] contain the user specific data.
+> All languages that are configured in the previous step in [languages.json] need an entry in each of these files.
+> For the definition of the obejcts to define refer to [model.ts].
+> 
+
 ## Development server
 
 Run `ng serve` for a dev server. Navigate to `http://localhost:4200/`. The application will automatically reload if you change any of the source files.
@@ -10,3 +32,7 @@ Run `ng serve` for a dev server. Navigate to `http://localhost:4200/`. The appli
 ## Build
 
 Run `ng build` to build the project. The build artifacts will be stored in the `dist/` directory.
+
+[src/data]: src/data
+[languages.json]: src/data/languages.json
+[model.ts]: src/app/data/model.ts
diff --git a/src/app/data/data.service.ts b/src/app/data/data.service.ts
index 1208917..ac2ebf7 100644
--- a/src/app/data/data.service.ts
+++ b/src/app/data/data.service.ts
@@ -39,8 +39,10 @@ export class DataService {
     lang = navigator.language;
     if (lang) {
       lang = lang.trim().split("-")[0];
-      this.setLang(lang);
-      return;
+      if (this.loadedLanguages.includes(lang)) {
+        this.setLang(lang);
+        return;
+      }
     }
     this.setLang(this.defaultLang);
   }