It is often assumed and sometimes explicitly stated that, with the introduction of memoQ version 6 and the new MQXLIFF and MQXLZ (a ZIP file with XLIFF and other resources) formats, memoQ has taken a step backward in compatibility and can no longer produce ordinary XLIFF (or *.xlf) files. This is simply not true!
Kilgray doesn't exactly help the situation by talking about renaming MQXLIFF extensions to XLF; in fact, I have roasted the chief developer of Kilgray slowly over hot coals for this and other silliness and told him how I think this all ought to be handled. (And knowing Gábor, when he does fix it, he'll exceed my best imagination in the quality of his concept.)
But as is often the case, those geeks at Kilgray actually solved the 'problem'; they just forgot their own solution or forgot how to explain it coherently.
First of all, it's important to get the settings right. In memoQ, XLIFF files are saved from the Documents or Views tab of Project home > Translations, by choosing Export bilingual, and the correct settings for the bilingual (XLIFF) file to be shared with other environments or older memoQ versions are:
When saving the file, simply change the file extension in the name of the file as you save it as shown here:
Now the file can be recognized without further ado and imported into most other environments for translation. The only real "troublemaker" here is, of course Trados. As I reported in September 2011, there is a bug in SDL Trados Studio which screws up the import of XLIFF files in many cases if the sublanguages are not specified or the default major languages do not match. SDL has many priorities, but often it seems that compatibility and standards compliance are not among them; to this day AFAIK the bug remains unresolved!
For users of other tools, this means that to exchange data with Trados users for any purpose, you should get in the habit of specifying sublanguages. This means DE-DE, DE-CH or DE-AT instead of DE for German, EN-US, EN-UK, and so on instead of EN for English. Ain't it great? Brought to you by SDL development. Maybe they'll do a better job once the move to Cluj, Romania is complete ;-)
Update 2013-07-24: Here is a short video illustrating the process of exporting XLF files from memoQ and opening them in SDL Trados Studio: