Reference to Sitecore's documentations and this related question, the 'Versions' tab in the Ribbon tag supposed to have the option 'Remove' to remove specific language version of the selected item, I have this option for most of the items, but in below scenario, after adding new language version to item, I can't find 'Remove' option:
Create Template 'Sample'-> Create Section 'Data' -> Add Field inside (which is item at the end) -> Add new language version of this field -> Here 'Remove' option will not be exist in 'Versions' tab.
Note: I've just added this version by mistake and just want to Undo it (remove this version).
You cannot remove version of templates, template sections and template fields using Content Editor.
You can use DB Browser application instead. You can open it using /sitecore/admin/dbbrowser.aspx url.
You will see Delete version button there.