In certain language versions of Windows 7, %windir%\Globalization\MCT contains one or more "MCT-XX" folders, with XX being a country code. They contain a theme and 6 wallpapers of scenery in that country. They're not installed by language packs, so the only way to get them is from installation media of the corresponding languages. (Windows Wallpaper Wiki page)

Windows XP Starter also has exclusive wallpapers. (Lost Media Wiki forum thread, My Digital Life forum thread, Windows Wallpaper Wiki page)

Windows NT 4 has a "Pan-Chinese Edition" with language code CHP. It's made for Hong Kong which needs to process both simplified and traditional Chinese characters. It's based on the Simplified Chinese edition, with the UI de-translated back to English. It's the only version of Windows as of 2024 to have a Jyutping IME builtin. (Microsoft did later provide a Jyutping IME in the zh-TW Office 2010 IME package.) The Jyutping IME is the only IME available during setup. It also contains "traditional Chinese Cangjie" (繁体仓颉) IME; both are by 北京中易电子公司, the same company as other Simplified Chinese input methods, and are made using the same framework as them as well. All input methods are under the zh-CN locale; there is none under zh-HK or zh-TW. (Chinese article, Official website)

Microsoft's own KB article suggests that NT 3.51 also has a Pan-Chinese edition, but I can't find any evidence of it actually existing.

Windows 95 RTM zh-CN contained Cangjie and Bopomofo IMEs, but they were removed in OSR1 and subsequent versions, because the tables of these IMEs contained taboo words. (Zhihu answer, BetaArchive forum post)