Problem adding new locale / Resaving matrix blocks Failed / Table 'matrixcontent_files' doesn't exist
I had a field called files, it did not belong to matrix. After deleting it (tried also simply renaming), the problem disappeared.

After that I created a field with the same name and that did not cause any problems.

Still do not know the exact reason, but later will have time dig a bit deeper, so if get some results will post them.