Sample text file: UTF-16 little-endian with BOM
Free sample from 99helpers.com/file-types/txt

Every character here takes at least two bytes. The file starts with the
byte order mark FF FE, which tells programs the encoding and byte order.
Line endings are CRLF. Windows Notepad calls this encoding "UTF-16 LE"
(older versions called it "Unicode").

If you see spaces or dots between all the letters, or the text looks
like Chinese, the program did not detect UTF-16.

Mixed scripts: English, Ελληνικά, Русский, العربية, עברית, 中文, 日本語
Outside the Basic Multilingual Plane (4 bytes, a surrogate pair): 😀 𝄞