In UltraEdit v20.00.0.1054 open Advanced - Configuration - File Handling - Unicode/UTF-8 Detection and make sure the configuration setting Auto detect UTF-8 files and best also Detect Unicode (UTF-16 files without BOM) are both enabled. The other two settings in this configuration dialog are usually unchecked because not needed whereby the last one unchecked saves some time on loading a file.

The encoding for new files can be set at Advanced - Configuration - Editor - New File Creation where you have to select Create new files as UTF-8.

The first two settings at Advanced - Configuration - File Handling - Save determine if UTF-8 files are by default saved without or with BOM if not selecting in File - Save As dialog a different encoding.

UTF-8 files containing only ASCII characters, i.e. characters with a code value smaller than 128 decimal, saved without byte order mark are binary equal to ANSI encoded file containing only ASCII characters. For that reason UltraEdit and any other application cannot automatically detect if the file should be interpreted as UTF-8 or as ANSI encoded file.

There is also the setting Force UTF-8=1 which can be manually added to uedit32.ini respectively uedit64.ini in directory %APPDATA%\IDMComp\UltraEdit with Windows Notepad while UltraEdit is not running in section [Settings] to interpret all non UTF-16 encoded files automatically as UTF-8 encoded files. But be aware that with this setting you must use File - Open and explicitly select ASCII/ANSI encoding when an ASCII/ANSI encoded file must be opened in UltraEdit. For more details on this special setting forcing single byte encoded text files to be interpreted as UTF-8 encoded files read the forum topics UTF-8 not recognized, largish file and Using UTF-8 with UltraEdit.

Please note that when you have once in the past manually selected a different code page / encoding for an active file from what was automatically detected by UltraEdit, UltraEdit remembers this setting for this specific file in its INI file. So the user has not to manually set the code page / encoding once again on opening this specific file again in a future UltraEdit editing session.

Close UltraEdit project or all open files, open Advanced - Settings or Configuration - Toolbars / Menus - Miscellaneous, click on button Clear history which clears all histories including the file specific code page history, click on button Cancel and exit UltraEdit. Restart UltraEdit and reopen the files or project.

There is no built-in support for clearing a specific history only. This must be done with Windows Notepad by editing the INI file while UltraEdit is not running if really wanted to be done. The section to delete is [File Code Page].