diff --git a/mercurial/subrepo.py b/mercurial/subrepo.py
--- a/mercurial/subrepo.py
+++ b/mercurial/subrepo.py
@@ -52,10 +52,12 @@ def submerge(repo, wctx, mctx, actx):
     sa = actx.substate
     sm = {}
 
+    repo.ui.debug("subrepo merge %s %s %s\n" % (wctx, mctx, actx))
+
     def debug(s, msg, r=""):
         if r:
             r = "%s:%s" % r
-        repo.ui.debug(_("  subrepo %s: %s %s\n") % (s, msg, r))
+        repo.ui.debug("  subrepo %s: %s %s\n" % (s, msg, r))
 
     for s, l in s1.items():
         if wctx.sub(s).dirty():
@@ -67,7 +69,7 @@ def submerge(repo, wctx, mctx, actx):
                 sm[s] = l
                 continue
             elif l == a: # other side changed
-                debug(s, _("other changed, get"), r)
+                debug(s, "other changed, get", r)
                 wctx.sub(s).get(r)
                 sm[s] = r
             elif l[0] != r[0]: # sources differ
@@ -76,33 +78,33 @@ def submerge(repo, wctx, mctx, actx):
                       'use (l)ocal source (%s) or (r)emote source (%s)?')
                       % (s, l[0], r[0]),
                       (_('&Local'), _('&Remote')), 0):
-                    debug(s, _("prompt changed, get"), r)
+                    debug(s, "prompt changed, get", r)
                     wctx.sub(s).get(r)
                     sm[s] = r
             elif l[1] == a[1]: # local side is unchanged
-                debug(s, _("other side changed, get"), r)
+                debug(s, "other side changed, get", r)
                 wctx.sub(s).get(r)
                 sm[s] = r
             else:
-                debug(s, _("both sides changed, merge with"), r)
+                debug(s, "both sides changed, merge with", r)
                 wctx.sub(s).merge(r)
                 sm[s] = l
         elif l == a: # remote removed, local unchanged
-            debug(s, _("remote removed, remove"))
+            debug(s, "remote removed, remove")
             wctx.sub(s).remove()
         else:
             if repo.ui.promptchoice(
                 _(' local changed subrepository %s which remote removed\n'
                   'use (c)hanged version or (d)elete?') % s,
                 (_('&Changed'), _('&Delete')), 0):
-                debug(s, _("prompt remove"))
+                debug(s, "prompt remove")
                 wctx.sub(s).remove()
 
     for s, r in s2.items():
         if s in s1:
             continue
         elif s not in sa:
-            debug(s, _("remote added, get"), r)
+            debug(s, "remote added, get", r)
             wctx.sub(s).get(r)
             sm[s] = r
         elif r != sa[s]:
@@ -110,7 +112,7 @@ def submerge(repo, wctx, mctx, actx):
                 _(' remote changed subrepository %s which local removed\n'
                   'use (c)hanged version or (d)elete?') % s,
                 (_('&Changed'), _('&Delete')), 0) == 0:
-                debug(s, _("prompt recreate"), r)
+                debug(s, "prompt recreate", r)
                 wctx.sub(s).get(r)
                 sm[s] = r
 
@@ -171,6 +173,7 @@ class hgsubrepo(object):
         return w.dirty() # working directory changed
 
     def commit(self, text, user, date):
+        self._repo.ui.debug("committing subrepo %s\n" % self._path)
         n = self._repo.commit(text, user, date)
         if not n:
             return self._repo['.'].hex() # different version checked out
@@ -196,6 +199,7 @@ class hgsubrepo(object):
     def get(self, state):
         self._get(state)
         source, revision = state
+        self._repo.ui.debug("getting subrepo %s\n" % self._path)
         hg.clean(self._repo, revision, False)
 
     def merge(self, state):
@@ -203,8 +207,10 @@ class hgsubrepo(object):
         cur = self._repo['.']
         dst = self._repo[state[1]]
         if dst.ancestor(cur) == cur:
+            self._repo.ui.debug("updating subrepo %s\n" % self._path)
             hg.update(self._repo, state[1])
         else:
+            self._repo.ui.debug("merging subrepo %s\n" % self._path)
             hg.merge(self._repo, state[1], remind=False)
 
     def push(self, force):