Geonames is a "linguistic geography" page: "The countries of the world in their local languages and scripts, with official names, capitals, flags, coats of arms, administrative divisions & subdivisions, national anthems, and translations of the country and capital names into many languages." It is worldwide in scope, and some of the information may be of use for reference for localization or writing locales.
The Geonames site includes some alphabet charts that have been referenced on appropriate Major Languages pages of this wiki (click "Backlinks" at the top of the left sidebar to see the languages linked). These are not necessarily authoritative, so should be compared with other data and verified before using. The charts are organized alphabetically by language: