Migrated from ppy/osu-resources#43. Since April, a few of the issues have been fixed. Here are the important ones which remain:
KH): The central band should be red and the outer bands should be blue, not vice versa.KM): As a symbol of Islam, the crescent (and stars) should probably not be distorted as they are.LK): The golden lion on the left side of the flag is completely missing.MR): The red stripes on the top and bottom are completely missing.MV): The center is completely incorrect. It should not be blue, it should be green.Alright, bodging
You can also add Turkey (TR) flag to the list.
It's a minor detail but the star should be rotated as shown in the picture below.







Fixed. Updated the repository.
Would like to add Philippines (PH) as well, last time I checked the white triangle at the left only has a yellow circle instead of the "Three Stars and a Sun"

(_just screenie'd discord's ph flag emoji_)
I'll list the remaining non-critical issues here for posterity:
AG): The sun should be a sixteen-pointed star rather than a circle.AL): The double-headed eagle should be black instead of white.AU): The Southern Cross (Crux constellation) has five stars as represented on the actual flag, and most of the six total stars on the flag are seven-pointed.BO): The coat of arms of Bolivia might be better represented than with a circle.BT): The bottom-right half of the flag should be orange, not red.CN): The four small stars should be pointed towards the larger star. The 2016 Summer Olympics at Rio failed to adhere to this.CR): The official ratio of the stripes is 1:1:2:1:1.CU): The stripes should be equally sized.CV): The official ratio of the stripes is 6:1:1:1:3, but having the central three stripes equally proportioned would be sufficient in my opinion. This might not work at this small a resolution, but there should also be ten stars.ES): Apparently, this simplification of the coat of arms could be considered offensive. I'm not Spanish, though, so take that with a grain of salt.ET): The emblem in the center of the flag is quite heavily emphasized by the government.FJ): The background of the flag should be a sky-blue rather than the navy seen in other similar flags.FM): The four stars should be pointing in each of the four cardinal directions.GB): The red saltire of St. Patrick should be offset. This isn't really offensive, but it does look silly to ignore.GY): This representation of the flag is rather wonky. All the triangles should be vertically centered and the white/yellow triangles should extend to the right side of the flag.IN): As a spiritual symbol, the Ashoka Chakra (the 24-spoked wheel) should probably not be simplified.IR): Whoops, I missed this one back in April. The emblem in the middle of the flag is actually a stylized rendition of the text "Allah," so it should definitely not be simplified.KR): The four black trigrams represent national values, but have been reduced to meaningless double lines.MA): As with Israel, the pentagram is a religious symbol (Seal of Solomon) and should not be simplified.PR): The coat of arms in the center is missing entirely.PH): As mentioned above, the emblem on the triangle is perhaps oversimplified.SZ): The emblem in the center should probably not be simplified as drastically as it is.TH): As with Costa Rica, the stripes' ratio is 1:1:2:1:1.TT): The stripe is going the wrong way.WS): As with Australia, the Southern Cross should have five stars.ZA): Like Guyana, the flag is slightly wonky. The lines should be of equal width throughout.ZW): The triangle on the left should be white.Here's a list of flags which currently stylize the star and/or crescent and maybe shouldn't:
AZ)LY)PK) maybe?wouldn't using twemoji opensource flags solve all the problems?
Yes, but Twemoji also has a markedly different visual style from the rest of the osu! website. Personally, I'm quite fond of the pastel coloring that the flags have.
The Mexican flag should probably use a darker green, a darker red and possibly a darker coat of arms too, because at first glance, it looks like the Italian one.
Will look into expanding the colour palette for the flags.
Trinidad and Tobago flag is backwards, would love for it to be fixed.
By backwards, do you mean they are applied to the wrong country?
Checked Trinidad and Tobago, and it's already fixed in the latest round of fixes.
Where are these fixes? Are they in a state we can deploy?
It's all in #Resources/Flags
Which folder? Also are the filenames supposed to be country names instead of acronyms?
To clarify: there's
Flags PNG
Flags PSD/flags_2-assets
New Flags PNG
New Flags PNG Small (is this supposed to be @1x?)
zip files maybe containing the same, maybe different to above
almost comical levels of what
There are only New Flags PNG and New Flags PNG Small (half the size, but it's not meant solely for @1x as I use it for some other small areas because when all of the designs were still done in Photoshop, it doesn't transform perfectly, because Adobe.)
Zip files are the resources for other designers to use. PSD, are the working files so I can edit/make new flags.
I'll just move the archives out of the folder.
Do you have a list of which flags have actually changed? And any idea why they have full country names not acronyms? We're going to have to go through and rename them to match again.
That's all from the original file; all the layers were in full names. I can't remember if I manually changed everything one by one, or someone else converted it to acronyms.
File names should be two lettered country code ("ISO 3166 code" section in Wikipedia), not the three letters version (which is mixed in in the 2x directory) ಠ_à²
The flag for TT (Trinidad and Tobago) is still going the wrong way. It should go like this: \ and not like this: /.
Current: 
Correct: 

This is the one that's fixed. It's in the folder.
Hmm that was confusing. Also I guess someone will have to rename them again.

The flag of Guinea - GN.png is wrongly arranged. The red color should be at the furthest left, with the yellow color being in the middle.
For reference, please see https://en.wikipedia.org/wiki/Flag_of_Guinea