Created attachment 301854 [details]
Test XML to reproduce problem

Both lxml and xmlstarlet fail to process XPath is root element is Cyrillic; or more precisely, if first letter of root is Cyrillic.

$ xmlstarlet sel -t -v "/юникод/text()" test.xml
Invalid expression: /юникод/text()
compilation error: element with-param
XSLT-with-param: Failed to compile select expression '/юникод/text()'

But this works:

$ xmlstarlet sel -t -v "/./юникод/text()" test.xml 
текст

It reproduces also in Python lxml

#!/usr/bin/env python3
import lxml.etree
e = lxml.etree.fromstring('<?xml version="1.0" encoding="UTF-8"?><юникод>текст</юникод>'.encode('utf-8'))
# Works
assert e.xpath('/./юникод/text()') == ['текст']
# Fails
assert e.xpath('/юникод/text()') == ['текст']