וַיֹּ֣אמֶר לָבָ֔ן לֹא־יֵעָשֶׂ֥ה כֵ֖ן בִּמְקוֹמֵ֑נוּ לָתֵ֥ת הַצְּעִירָ֖ה לִפְנֵ֥י הַבְּכִירָֽה׃
At sinabi ni Laban, “Hindi ginagawa ang ganyan sa aming lugar, na ibigay ang nakababata bago ang panganay.”
Sforno
It is not done in our place. Lavan claimed that the people would not allow him to keep his word, since it was in violation of local custom.
Or HaChaim
ויאמר לבן לא יעשה כן במקומנו. Laban said: "This is not the way things are done in our place, etc." How could Laban expect now to get away with such an explanation when he and Jacob had entered into a specific agreement that Rachel was to be given to Jacob? Why would local customs override such an agreement?
Radak
ויאמר...לא יעשה כן במקומנו, even though you asked for the hand of my younger daughter in marriage, seeing that apparently where you come from it does not matter if the younger sister gets married before the older one, in our place that is not a permissible procedure. I will therefore give you both of them with the proviso that the nuptials of the older one must precede those of the younger one.