Hi @Nata M,
They are actually same. As @A T mentioned, it is related to your visitors' browser/os. Normally, first 2 letter describes the generic name of the language and the other ones specifies the language origin(Such as us english, uk english etc.). Some browser/OS combinations assigns different values as the language code. Since Google Analytics grabs this data from browser, it gets whatever is set as user's language.
I hope this helps.