Fix removes the error that prevented the "replacement" of files with one that has a modern extension, and vice-versa. However, it does not actually replace the file in question; it just adds the new file to the list of files for the course. This may be because there are references to said file that must be altered before the file can be fully replaced. Further discussion might be needed to decide how to tackle this problem.

Changes look good, great work! The only thing I would argue to add is a note mentioning that taking a look at the file and saving it as a docx, pptx, xlsx, etc, and re-uploading it, could fix the issue. Why I would add this note is because there's no way to replace a modern file with one that has the old extension. The alternative to this, is allowing them to replace modern filetypes with older filetypes, but we don't want to encourage that.

Lastly, good call adding the message in the english translation. I can add a similar one to the spanish translation, if it needs it.