He wants to wear the Arabic thawb in a non-Muslim country
I've read the other fatwas concerning this matter but I couldn't find anything related to the permissibility of wearing a thawb in situations like this.
What is prescribed is for the Muslim to wear the customary clothing of the people of the country in which he is living, so that he will not stand out among them in ways that may harm him or attract backbiting about him, so long as that clothing does not include anything that is contrary to sharee‘ah.
So long as the Arabic thawb is regarded as foreign or strange in a country and is not acceptable, it is better for you to wear what is customary for the people in your country, whilst making sure that the pants are loose and do not show the shape of the ‘awrah.
Shaykh al-Islam Ibn Taymiyah (may Allah have mercy on him) said:
If a Muslim is in a non-Muslim land that is hostile towards the Muslims, or a non-Muslim land that is not hostile, he is not enjoined to differ from them in his outward appearance, because of the harmful consequences that may result from that.
Rather it may be mustahabb or obligatory for a man to be similar to them in his outward appearance sometimes, if there is a religious interest to be served by that, such as calling them to Islam and other good aims.
But in Muslim lands where Allah has caused His religion to prevail and has caused the disbelievers to come under Muslim rule and pay the jizyah, it is prescribed to be different from (the disbelievers in appearance).
End quote from Iqtida’ al-Siraat al-Mustaqeem, 1/471-472.
And Allah knows best.