Veronica Loell's "Mimers brunn" [L1 ] project includes a message extractor for use with msgcat. It also knows how to translate to the po-format of GNU gettext.
An few example tcl-rows:
.lblfileName configure -text\
[::msgcat::mc "Make sure that the folder you want to repair\n\
is not currently in use, and then select it by clicking 'Select folder'."];#! This is a message to the translator
Will produce the following entry:
#. widget: label - This is a message to the translator #: src/uidrebuild.tcl:33 ::msgcat::mcset sv\ "Make sure that the folder you want to repair\n\ is not currently in use, and then select it by clicking 'Select folder'."\ \