I returned to a site designed months ago, and added a second language to it.
From the beginning, this site had prominent composition of entries out of multiple elements in their matrix, with formatting choices selectable on the elements (like positioning and size for images; or position left or right for compound pull quote/citation blocks.
This all works fine, and now in languages. However, there is the fact that languages other than the first used seem
not ever never to have their Matrix of content blocks copied over into the new language. The Matrix is there, of course, but empty.
This emptiness is the case with first save starting with an entirely fresh entry, which is a noted in the add as the only case at present where Craft normally copies content to other available languages, and very handily so.
Really I think this is a bug report, but maybe not?
At present copy over does, as commented below, operate only at the point of first save to a first language. If you edit after saving, only that first save will have been copied, and your edits won't be. If you add fields to the section, and fill them in for a first language, nothing will be copied for those to other languages.
This is clearly worth looking into for persons who use multiple languages/Locales, but isn't so simple to do well, and I believe it is somewhere down the list for Craft futures, likely properly so compared other desires. Worth mentioning, though ;)