Okay, well that’s simplier than UCS-2 from SMS via AT. Your the Huawai modem is doing you a favor here - most modems give you an SMS PDU that requires parsing before you even get to the UCS2.
Your “:local content” variable should already have UTF-8 in it (e.g. the XML metadata <?xml version="1.0" encoding="UTF-8"?>). So you just need to use a different @rextended function with the $content (e.g. [$fURLEncode $content]) before passing it along to telegram:
http://forum.mikrotik.com/t/replace-characters-in-string-url-encode/76863/11
To get the raw UTF-8 bytes into the urlencoded string (e.g. UTF-8 that’s % encoded for use in the HTTP query string).
RouterOS only allows you parse the bytes involved in unicode, but it really doesn’t haven’t unicode support for display/input in CLI/winbox/SSH/etc.