Section 20. - Foreigners enjoy within the territory of the Nation all the civil rights of citizens; they may exercise their industry, trade and profession; own real property, buy and sell it; navigate the rivers and coasts; practice freely their religion; make wills and marry under the laws. They are not obliged to accept citizenship nor to pay extraordinary compulsory taxes. They may obtain naturalization papers residing two uninterrupted years in the Nation; but the authorities may shorten this term in favor of those so requesting it, alleging and proving services rendered to the Republic.