Exactly.
Maybe this winter when I have more time…
Sure. We will wait for you, Master.
Just use ASCII latin characters. Why is that an issue? Translit is a thing.
This is not a problem, but a desire. 
You run into this issue even if you have a valid UCS-2 PDU:
http://forum.mikrotik.com/t/support-sms-text-mode-at-cmgf-1/32067/1
Even a perfectly PDU encoding isn’t going to be helpful in “/tool sms” to SEND, since before the “message” in PDU there is a flag with the encoding. And Mikrotik is always declaring the message as ASCII (GSM7) in the PDU its building internally, so encoding the message= is likely not going to work. Maybe if MBIM is used, the message can be UCS-2, but doubt it.
And, if you use AT command to send, the PDU entry mode creates a “command prompt” needing a specific sequence that cannot be done with /interface lte at-chat [find] input=“…” – AT+CMGF=1 needs a specific sequence since there is a "> " prompt that appears.
The encoding is one step, but has to get into the modem somehow…
It’s clear. So this is not possible with the help of the script. This can only be implemented by the developers of the Router OS, but they will not do this, since it is necessary to support not only the Russian language, but also all other national languages. Although they could make it possible to install one national language in Ros in addition to English.
And then each user could additionally set their own national language.
Send
AT+CMGS=12
[12 is the length of the PDU 1 Byte (2 octects) less]
and wait for "> "
then send
0021000181F1001104F4F29C0E\0x1a
(\0x1a = message end)
done.
But… but… but…
Yes, but sends that from the CLI probably. And from a script?
That’s the problem…
Until someone find a way to send a test one,
it is completely useless to recode/create the PDU…
It’s the “wait for” part that isn’t possible… the at-chat add \n (maybe \r\n) and waits for OK. You can say not wait (wait=no), but still won’t help since you do need to wait for the “SMS text mode” and there is a specific control codes that prevent splitting into two commands. And SMS PDU is build before you get to message= in /tool/sms.
I’m still not sure why some encoding=ucs2 option be difficult in /tool/sms. Now multi-lingual RouterOS, that I’m not expecting. Setting one byte (actually less, half-byte/semi-octet) in one command seems doable & allowing a message like “\00\80\00\80” to passthrough. Not saying it should be top priority, but they are pitching IoT devices & sell to many non-English countries.
And, BTW, it’s also poor “emoji people” 
that are effected 
— which you can’t send either, since they’re unicode (and require similar UCS2 treatment).
Now multi-lingual RouterOS
no, a multilingual OS router is not needed, you only need the ability to install support packages for national languages to send SMS