Hi noorrru_,
Thanks for using Apple Support Communities! We see you ave a question about your iPhone showing WLAN as opposed to Wi-Fi, and we'd like to do our best to answer.
It sounds like your iPhone was originally manufactured in another country, as the descriptions used will be for the origin of the iPhone.
There isn't any issue with showing Wi-Fi or WLAN, as they mean the same thing, and function the same.
You can compare screenshots in this article with an United States version, which shows Wi-Fi to the same article for Germany, where it shows WLAN:
Connect to Wi-Fi on your iPhone, iPad, or iPod touch
WLAN-Verbindung auf dem iPhone, iPad oder iPod touch herstellen
Take care!