Every language has it's own unique name for a place. That place may be named after a tribe, a god, or whatever. For example, Hungary is called "Macaristan/Madjaristan" in Turkish and Persian because it's named after the Magyar tribe who settled in the Carpathian Basin and became founders of the Hungarian state. I usually use wiktionary.org to search for etymologies of English and foreign words. However out of interest I couldn't find the origin of "لهستان". I would like someone who's knowledgeable of both history and linguistics to answer this question.
Lech is the mythical founder of Poland and Laehae is simply Persianisation (?) of his name. The suffix -stan mean the land of, or the land of the people of. In this case Laehaestan translates as the Land of the People of Lech. Poland is referred to as Lechistan elsewhere, I know for instance Jan Sobieski III was know by the Ottomans as the Lion of Lechistan.
You may be interested to know -Stan exists in Old English and is preserved in certain place names in England. The word "saete" literally mean the land/place of X or the Land of the People of X. Any places in England which end in -set, like Dorset or Somerset, are preservations of this but for whatever reason -saete proved to be less widespread that -land. I'm not sure of the origins beyond this but they certainly come from the same root word.
Out of the medieval tribes that coalesced into early Poland, Lędzianie (Lenngians, probably descended from ancient Lugii) were the biggest and most South-East one. Therefore, for many nations and peoples from Asia and South/East Europe, the first (and often only) contact with medieval Poles was through Lędzians.
The name was the bastardized from Ledzianie to Lendizi and then to Lechchi/Lachi. Since the main Polish tribe at the time (Gnesnans, later renamed Polans) was a central one, separated from non-slavic neighbours from all sides, the name "Poland" did not surface for another several centuries after "Lechia" came to be used in the East. You can actually map the early relationship between Poland and its neighbours by this naming convention: variations of Pol- would be where there were official dyplomatic relations, variations of Lech- would be where there were pre-centralisation conquests and trade relations.
Source: Labuda, G. Czechy, Rus i kraj Ledzian w drugiej potowie X wieku. Labuda G. Studia nad poczatkami panstwa polskiego.
Lechia is an old term for ancient Poland, of course Poland did not exist as we know it at the time, but the people were aware of a shared cultural, linguistic and genetic heritage and this term broadly refers to that. Some early sources refer to Poland as the land of lech and your query might relate to that. Poland became more associated as a term for this geographic area and people as the polanie tribe became the more dominant tribe in the region.