It depends on the character set used on your page. I would always try to use UTF-8 when building a webpage. That would mean that the page would have the following header:
Content-Type: text/html; charset=UTF-8
In that case, it is fine to use the actual characters anywhere in the page, including in the meta tags:
<meta name=description content="My name is совестью">
If your page were in a character set that does not support all unicode characters such as ISO-8859-1, then you would have to fall back to using character entities like
ç. If possible, it would be better to use UTF-8 because the character entities increase the page size quite a bit if they are heavily used.
You should never have to substitute other characters that look similar. Search engines today are Unicode aware. They should have no problem understanding words in any alphabet that are placed into meta descriptions.