PANGO_TEXT_TRANSFORM_UPPERCASE parameters start and end are bytes in the text string not utf8 code points.
When we add a text-transform attribute on a GtkLabel and set the attribute type to be PANGO_TEXT_TRANSFORM_UPPERCASE, the start and end parameters of the attribute are interpreted as bytes in the text string, not utf8 codepoints.
For this reason, for some non-US alphabets, when we want to capitalize the first letter of the label text using Pango attributes, we get a question mark as the second letter.
For the string "Сценарий shell" we are getting "С�ценарий shell" displayed.