The error
XML Parsing Error: syntax error
Location: https://cxserver.wikimedia.org/v2/page/en/pt/Circle%E2%80%93ellipse_problem
Line Number 1, Column 1:
appears in the console when I access
https://pt.wikipedia.org/wiki/Special:ContentTranslation?page=Circle%E2%80%93ellipse+problem&from=en&to=pt&targettitle&campaign=interlanguagelink
from the English Wikipedia sidebar link, and the special page shows "Critical error: Content translation failed to load due to internal error", followed by blank spaces where the source and target language texts would be.
The page https://cxserver.wikimedia.org/v2/page/en/pt/Circle%E2%80%93ellipse_problem shows the following:
Page en:Circle–ellipse_problem could not be found. Error: Sectionwrap: Attempting to remove a non-section tag: undefined