Then maybe modal keymap is not the proper term, but I’m sure many messages aren’t extracted. What I’m referring to is this, which appears during transform:

Here, the messages that do get translated with my change (e.g. “Déplacer”) were extracted from entirely different sources. “Snap Invert” is not in the .po files under any context. It comes from editors/transform/transform.c and looks like this, which I don’t think is handled currently:

{TFM_MODAL_SNAP_INV_ON, "SNAP_INV_ON", 0, "Snap Invert", ""},

So I believe the regex is still useful, but now you mention it, maybe it should get a context, and then the TIP_() change below is wrong. However I couldn’t yet find out how to use regexps to extract messages from the source with a context, if it’s not explicitly specified there, as the macros do. I’ll keep trying.

Damn, my bad!

Ok so I found a way to override the context in the regex but it involves changing PYGETTEXT_KEYWORDS from a tuple of patterns to a tuple of (pattern, context) tuples, with context potentially None. So you get:

PYGETTEXT_KEYWORDS = (() +
    tuple(((r"<pattern>" + _msg_re + r"<pattern>").format(it),
           None)
          for it in ("IFACE_", "TIP_", "DATA_", "N_")) +

...

    tuple(((r"<pattern>" + _msg_re + r"<pattern>").format(it),
           bpy.app.translations.contexts.id_windowmanager)
          for it in ("_MODAL_",)) +

Not sure it’s either truly needed or the best way to proceed.