Hi holkfoor,
Your Sand Five SLiM theme here:
http://hg.slitaz.org/wok/rev/bc9334796734
http://cook.slitaz.org/cooker.cgi?pkg=slim-theme-sandfive
Asking your question — now all SLiM themes (with or without "strings" file) works with multiple languages support. It can use default translations: http://hg.slitaz.org/wok/rev/bc9334796734#l13.20
And still theme receipt should contains post_install and pre_remove functions like here: http://cook.slitaz.org/cooker.cgi?receipt=slim-theme-sandfive
Ok, I not forgot, I should make GTK+ theme and TazPanel theme too.