Comment 16 for bug 1249423

Based on my testing in Inkscape 0.91 stable in Windows, <switch> and systemLanguage work correctly when the user has explicitly set a UI language, but still do not work if the language is set to "use system default". In that case, all the language tests fail even if the system language is something that should match.

For reference, the language switching code is in conditions.cpp, which uses SPDocument.getLanguage() (document.cpp) to find the user's preferred language.