I am collaborating on the OpenStreetMap Wiki Spanish translation. A lot of English articles of the OSM Wiki need a translation into Spanish. They are too many so I think that the best option is to choose the most important pages first, or those another articles that are more attractive depending on personal interests of each one (e. g., pages related to hiking, or mountain biking).
One of the first tasks that I did it was to translate the categories into Spanish following the wiki conventions. Most of people are using the OSM wiki to get help about a particular subject, so a suitable order for the documentation is as important as the translation itself.