The time to drop that support is long passed. UTF-8 has won, the value of pandering to these ancient codepages versus the cost of choking and displaying mojibake just because someone dared to add a kanji character to a CSV should be clear by now.
For programming it's UTF8, except for Windows-centric developers (and Microsoft technologies).
Java uses WTF16 internally but rarely assumes an external charset, and when it does, older API tend to use the default charset (which is generally ascii-compatible at best: on western windows it's commonly windows-1252, though it's been UTF-8 for years on most unices). Newer APIs like Files.newBufferedReader(Path) straight go with UTF-8.