I decided to avoid buying clothes that have a non negligible probability of being made in on-ethical conditions, e.g. by people younger than 15 years old, or working more than 12h a days. When not buying in ethical shops, I look at the label and see the "Made in ..." information.
My question is, which countries are acceptable ? All EU seems acceptable to me, and US as well, but besides I don't know. Is Mexico or North-African countries little likely to host sweatshops, or is it a big problem ? I heard that Turkey used to be very bad but passed some law to secure the workers, but I don't know if they are really applied. East Asia is definitly a no-no.