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I'm not a pro at foreign language SEO but I just used Google's keyword tool to find out that ropa premamá gets 260 exact matches and ropa premama gets 9900 exact matches.  I personally would change the keyword to the non accent version simply on a keyword basis. On a side-note, there was a great MOZinar last week on Foreign Language SEO.  Might be something worth taking the time to look at. http://www.seomoz.org/webinars/foreign-language-seo