As he included the qualifier “ (yet)”, we can presumably infer that Firecore intends to make this feature multilingual in the (near?) future.
Frankly I just don’t understand how something so functionally inconsequential as whether the season title of a single-season series is displayed as “season 1” or “miniseries” got rolled out before so many other highly anticipated, long-roadmapped and oft-pushed-back features that would actually improve and/or fix the app’s core functionality … but such is the way of things around here.
Items in Emby/Jellyfin which are fetched from TMDB have a standard ‘Mini-series’ tag in on the server which is not visible (or editable) in the UI, but can be read by Infuse. This is a language neutral tag, so it will work no matter the language your server/device is set to use.
Adding support for additional ways to manually tag items as miniseries isn’t planned at the moment.