If I run ComicRack 0.9.125 in Portuguese language, no ComicInfo.xml files are added to my eComics if I run the "Update all eComic files" option (despite the fact that the program removes the so-called-processed files from the queue), but if I run the same version in English language, all works fine (obviously only on the new pending files).

Please take a look at this issue and add an option to force to update all eComics files even no need to update files is detected by the program

Now I've found that cbr/cbz files with no files at root folder (file.cbr/randon_name/000.jpg etc) don't have the ComicInfo.xml file added.

.cbr's won't have ComicInfo.xml's in them, the file format is proprietary and won't allow packaging without an extremely expensive licence.

Only .cbz's with have ComicInfo.xml embedded inside them.

You can force an update to files by rerunning the ComicVine script on them, re-exporting them to .cbz, opening them and reading them, or by selecting all the comics in a Stack, right clicking them and opening info, then clicking OK.

The language ComicRack is in should have no effect at all on this behavior. Lanaguage packs simple replace menu/display text, they don't change the programs behavior at all.