Localisation issues on the analytics screen
I'm using Twitch in Swedish, primarily for the Swedish formats since English (Sweden) isn't an option.
But there are some improper formats on the analytic screen, and this issue is likely happening to several other languages, and is likely due to hardcoded functions. By resolving these issues, these are not only resolved for Swedish, but also for several other languages.
When you press on the date-banner at the top to change the date, the date-pickers are displaying with Sunday first, which is quite confusing to look at since Sweden is always Monday first. This calendar should reflect the locale chosen. When grouping days by weeks, the weeks are Sunday-Saturday. To me this is like displaying 31 March–29 April. The locale should determine which days are grouped.
The streamed time is written as "1 h, 59 m" which is also improper. I suggest not using a comma, since it isn't necessary for combined units, and use the proper symbol "min". While it is unambiguous here, it's still good to be consistent and correct. "m" is metre, "min" is minute. It should use the CLDR narrow symbols for hour and minute here and combined using CLDR narrow unit list (displaying list), so that's "1 h 59 min" in Swedish, "1 hr 59 min" in English, "1 Std., 59 Min." in German, and so on.
Then the Swedish translation is "Tittare i snitt:Kanal", which does reflect the formatting of other languages. But I would suggest writing this as "Tittare i snitt/kanal" to follow the standard usage of / to mean "per". Then the translation "Uppskattad bläddringsplats" is too long, and I would suggest shorten it to "Uppsk. bläddringsplats", where "uppsk." is a common abbreviation.
This page also uses the short year-format for the achievements that I don't like, and is also not official. It shouldn't say 23-04-10 but rather 2023-04-10. There's one way to write it with an abbreviated year in Swedish by writing 10/4-23 (d/M-yy) but I still think you should use the proper date-format here regardless.
On the page /settings/revenue/leaderboards there is a translation error, but it might as well be the same timezone-issue as listed elsewhere.
In the Swedish translation, it states "nollställs automatiskt varje dag kl 12:00 PT" (resets automatically each day at 12:00 PT), but "PT" is not a valid code in Swedish. I know it is North American Pacific Time, but not only should it localise the code ("UTC-7") but it should rather give it in my timezone, which is 21:00 CEST/CET (and 20:00 CET during the few weeks). Even better would be if the time this resets is based on the streamers timezone instead.
On the page /settings/revenue/subscription/badges it also has an issue with dates. It also crops the year down to 2-digits unnecessarily. So it would say 23-05-01 instead of 2023-05-01, despite there being plenty of space, because the word "Grundläggande" fits.
Further issues on the dashboard can for example be found on /settings/channel/stream-events where you can set the date for the anniversary, and the date is forced to the format "MMMM dd, y" with English regardless of locale. So it will say "May 01, 2023" even in Swedish, but it should say "1 maj 2023" in Swedish.
A weird bug is also that when I choose a date, it will pick one day earlier. So if I pick 3 May, in the date-picker, the field then say "May 02". This might be a timezone issue where I choose "3 May 00:00 CEST" which then is 2 May in UTC and in USA, which could be the reason why?
Also, the Swedish translation for "N/A" is "E/T" which is a non-standard translation and I had to check what the English wording was to get what it means. An actual established abbreviation in Swedish is "i.u.", but there is no problem writing out the full "Ej tillgänglig" or "Ingen uppgift" since there's plenty of space for that.