# If you'd like to omit non-matching lines from the result; add ';d' to the end of the expression.
sed -E 's/(?<=\{\{Infobox(?:[^{}]|\{\{(?:[^{}]|\{\{[^{}]*\}\})*\}\})*)\[\[ *(?:image|fi(?:le|chier)) *: *([^\|\]]*)[^\]]*\]\]/$1/gmi;t' <<< "{{Infobox xyz
|aaa= Xyz {{foo| {{A NESTED TEMPLATE}} other stuff}}
|bbb= [[Xyz]]
|ccc=[[File:xyz.jpg|thumb|Xyz.]]
|bbb= [[Xyz]]
|ccc=[[Image:xyz.jpg|thumb|Xyz.]]
|ddd= {{lang|en|xyz}}
}}
[[File:abc.jpg|thumb|Abc.]]"
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for SED, please visit: https://www.gnu.org/software/sed/manual/html_node/The-_0022s_0022-Command.html