ThreadFreedom of speech debate heats up in France after death threats to 16-year-old girl who called Islam "religion of hate"
You're right that Islam's origin in Arabia means that some aspects of Arabic culture come along with it. I'm not an Arab, but I can read the Arabic alphabet (most Muslims are taught how to read the Quran in Arabic and even memorise portions - or the entirety of it - from childhood), was encouraged to learn Arabic and did for many years (still interested in picking it back up as it's a very beautiful language). The five daily prayers are said in Arabic, and there are a number of supplications that you say in Arabic too. There are certain foods that are common in a number of countries during Ramadan, too. Depending on how religious the person is, they might wear Arabic clothes, but really each country has their own form of 'modest' Islamic clothing, and that is what is generally worn in each country. It even varies in different Arabic/Middle Eastern countries.
All of this is separate from ethnicity, though. I've never met an ex-Muslim who still considers themselves a Muslim in any form. Typically if they still practice some of the customs, it's due to peer pressure from their families, since a lot of people cannot come out and say "I've left Islam" without facing some form of repercussions, even if it's just a huge strain with their family. Muslim as a label is very strongly tied to belief unlike Judaism. You may hold on to some of the values you learned from Islam (as there are honestly a lot of positive teachings, Islam definitely had a part in informing my views on class for example, and why I always found religious conservatives who hate the poor perplexing), but if you don't believe in Allah at the very minimum, then that direct link to the faith is broken.
I'm not sure about what you mean about who is suitable for increasing the numbers of the religious followers (in relation to Islam, at least).