In a Hadith to the nearest meaning, hte Prophet PBUH said, “Whoever imitates a nation is from amongst them.” (‘Man ta shabbaha bi qawmin fahowa minhum’). Is this imitating the Kuffaar.
With regard to pants and shirt, this mode of dressing has not been adopted by the learned and Allah-fearing, hence, attiring oneself in this fashion is not desirable. Moreover, a person would be deprived of the reward he would attain by adopting the Sunnah mode of attire. (Fataawa Mahmoodiyyah, vol.17 pg.349; Mahmoodiyyah)
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai