I don't have OpenBSD, but to check if a file is UTF-8, try this:
file -i filename.txt
The command should tell you the charset information, and if it's UTF-8, it should say something like "charset=utf-8."
The file command might still label UTF-8 files as ASCII text due to its classification rules (UTF-8 is an extension of the ASCII character set).
That result doesn't necessarily mean there's something wrong with your system setup.