Xliff Editor - its fast to load, easy to use, and has a low memory footprint. It has Inline tag protection, Search & Replace, Regex search, Fuzzy search, intuitive shortcuts, multiple concurrent file editing, native spell checker, Alternate translations and can read even the most complex Xliff v1.2 files.
An xliff file is a standardized file format based on XML, used to represent localization data. In its simplest form the original(source) string is stored as well as its translated(target) complement. Xliff files enable localization to be much more user friendly, and less error prone than manual translation. Xliff files can be identified by the extensions .xliff or .xlf. SDL Trados (.sdlxliff) also uses the xliff format, but includes some extra proprietry data.
Xcode 6 introduced the ability to export/import all your localisation data, taking away the need for sending various file formats to your localisers for translating. The XLIFF format makes translating a cinch, as it removes all the layout and formatting, and just provides a simple text-to-text translation mechanism for your translators.