take skin language from skin_language key

before using this function skin_language varaible should declared with
supported value  fr, en, de, es, it
- 1 - enter in the browser http://localhost:8888/yamj3/config/list.html
- 2 -click on enter new configuration ()
- 3 - enter skin_language as key
- 4 - enter a valid value language as value
- 5 - click enter