Make PO files compilation work properly

Author: patrickfournier

po/POTFILES.in

@@ -0,0 +1,5 @@
+To add a new translation:
+
+- Add the language code to the `LINGUAS` file
+- Add the .po file to the `po_files` list in `meson.build`
+- Build the `update_all_po` target to create the new .po file