Metaphor's advice is to judge the importance of each market for your business, both in your current operations and in your plans for expansion in the future. If sales in South America are key for you, then your online marketing department is going to need to learn which are the most popular search engines in your key markets and whether they search global TLDs with the same priority as the local country code TLDs (for example, Argentina is .ar, Brazil is .br, Paraguay is .py). Another consideration is the status of local registration of a domain name in establishing trademark registerability.
Beyond registering your domain name, there are, of course, other things to consider in establishing an international online presence. For more on verbally taking your brand international, please see Metaphor's Global Perspective white paper.
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