I just tested this, and it works fine for me. Are you sure the tool you’re using to edit the image metadata isn’t the problem? I used exiftool to add the relevant tags. To be clear, these are the XMP dc:description and dc:title tags, as defined here: XMP - Dublin Core Schema.
It would help if you could post the complete XMP data from an example image that demonstrates the problem (i.e. as produced by the tool you use for editing the title/description). In particular, it would be interesting to see the values of the xml:lang attributes (if any).
The exact exiftool command I used for setting the tags was:
exiftool -xmp:Description='Мой комментарий' -xmp:Title='Мой комментарий' test.jpg
which produces the following embedded XMP data:
<rdf:RDF xmlns:rdf='http://www.w3.org/1999/02/22-rdf-syntax-ns#'>
<rdf:Description rdf:about=''
xmlns:dc='http://purl.org/dc/elements/1.1/'>
<dc:description>
<rdf:Alt>
<rdf:li xml:lang='x-default'>Мой комментарий</rdf:li>
</rdf:Alt>
</dc:description>
<dc:title>
<rdf:Alt>
<rdf:li xml:lang='x-default'>Мой комментарий</rdf:li>
</rdf:Alt>
</dc:title>
</rdf:Description>
</rdf:RDF>
The data can be exported with exiftool like this:
exiftool -xmp -b test.jpg
After uploading to iNaturalist, I see this:
