XLIFF (XML Localization Interchange File Format) is the OASIS standard XML format for bilingual translation files, in which a CAT tool stores each source segment with its translation, status and notes, separate from the original document's layout.
Translators rarely translate a Word file, a website or an app's strings directly. A CAT tool or a developer's tool first extracts the text into an XLIFF file, the translation happens there, and the translated XLIFF is then merged back into the original format. Because the layout stays outside the XLIFF, the translator cannot break it.
Each segment in the file holds the source, the target (empty until translated), a status such as new, translated or final, and optional notes. Formatting inside a sentence is kept as tags that must survive in the translation.
XLIFF 1.2 and XLIFF 2 are both in use, and most CAT tools still build on 1.2. Several tools save their own flavour of it:
They add tool-specific data, such as match scores and segment locks, so they open fully in the tool that made them and partly elsewhere. memoQ, for example, opens SDLXLIFF files from Trados.
XLIFF is the working file for one job. TMX carries the translation memory built from many jobs, and TBX carries terminology from a termbase. Our post on XLIFF, TMX and TBX explains the three side by side.
An agency sends you a Trados package with a user manual as SDLXLIFF. You translate it in your CAT tool, then, before returning it, you run a QA check: numbers, tags, terminology and punctuation, segment by segment. The agency imports the SDLXLIFF back into Trados and generates the translated manual with its original layout.
TraduQ's free tools read XLIFF in the browser, without uploading it: the QA checker for XLIFF, SDLXLIFF, MQXLIFF and MQXLZ, the converter to review a file as an Excel sheet, and the word count and quote tool. See how to QA check XLIFF files.