Consider tonight the deadline
(midnight, UTC -7, 12 hours after this edit)
Sometime tomorrow afternoon the devs are going to put together the builds for the different platforms so they'll be ready for the release on Saturday. Any translation that isn't in by then will have to wait for the next release.
The next release is coming soon, and there are some strings that need to be translated for each language.
I have put together lists of what needs to be translated for the _fallback and default themes in two zip files.
The list of what is missing from each language is in "<language>_missing.ini", where "<language>" is the name of the language. So the strings that are missing from the Polish translation are in "pl_missing.ini".
Strings that are (probably) unused are in "<language>_unused.ini". This assumes that anything not in the English language file is not used.
List of languages with existing translations:
If you can provide a fluent translation of the missing strings for a language, please do so, and your name will be added to the credits under the list of translators. You can submit the updated language file either by opening a pull request or issue on Stepmania's github page
or by posting a link to it in this thread.
Jarosław Pietras is currently handling the Polish translation.
If you are a themer and you wish to know what strings in your personal theme need to be translated, the lua function for generating the lists is in _fallback/Scripts/find_missing_lang_strings.lua
(as of 5 minutes ago, you'll have to download it from github and add it to your local copy) and you just need to call the lua function with the name of your theme and the name of the language file that is a complete translation, like this: