After some debugging, I realized that the whole thing executes with
default-directory set to "c:/blah/blah/blah/ê/trunk/" the following
two commands:

 (process-file "svn" nil t nil "--non-interactive" "status" "-v" "ê.tex")

and then:

 (process-file "svn" nil t nil "--non-interactive" "cat" "ê.tex")

The first command works quite fine, but the second one fails, and having
a look info the " *temp*" buffer, I saw that svn angrilly barks with
some error message like this one: