How do I get Matrix elements to copy their content across language Locales? 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?

Add: 

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 ;)
Ok, in some conversation with Brandon which leaned this direction, I realized a different direction to temporarily solving most of this problem.

It turns out that a root of the issues is that marking a Matrix as translatable causes the base problem here, that the set of elements in an original language isn't copying at all into other Locales, as would be expected on first Save as all other kinds of elements do.

If you don't mark the Matrix as translatable, two good things happen:


All Matrix elements now do get copied over, so that you don't have to recreate the Matrix in its individual form for each Entry and language.
Text items marked as translatable do have their original text copied over, so that you have a starting situation for language translation


It's true that Assets marked as translatable show up empty rather than with their original content, but at least they are there.

We also don't really know what marking a Matrix as translatable should mean. I suspect it should mean that all contained elements are marked translatable, but we shall see.

The Craft crew is well aware of issues here, and plans a careful improvement of the whole area, which as complex isn't at the top of lists yet. 

This little detail should get most of us through until that happens, and given we set up the non-translatability of Matrix elements, should make extra steps explainable to customer end users.