The SVN url has been changed by SourceForge. In your repository root, or in an individual module, run the command:
svn switch --relocate https://apertium.svn.sourceforge.net/svnroot/apertium/ https://svn.code.sf.net/p/apertium/svn/
Pages that link to "Category:Serbo-Croatian and Slovenian"
From Apertium
No pages link to Category:Serbo-Croatian and Slovenian.

