--- a/mercurial/filemerge.py	Sat May 13 03:28:36 2017 +0900
+++ b/mercurial/filemerge.py	Sat May 13 03:28:36 2017 +0900
@@ -133,7 +133,7 @@
     def check(tool, pat, symlink, binary, changedelete):
         tmsg = tool
         if pat:
-            tmsg += " specified for " + pat
+            tmsg = _("%s (for pattern %s)") % (tool, pat)
         if not _findtool(ui, tool):
             if pat: # explicitly requested tool deserves a warning
                 ui.warn(_("couldn't find merge tool %s\n") % tmsg)

--- a/tests/test-merge-tools.t	Sat May 13 03:28:36 2017 +0900
+++ b/tests/test-merge-tools.t	Sat May 13 03:28:36 2017 +0900
@@ -392,9 +392,9 @@
   true.executable=cat
   # hg update -C 1
   $ hg merge -r 2 --config merge-patterns.f=true --config merge-tools.true.executable=nonexistentmergetool
-  couldn't find merge tool true specified for f
+  couldn't find merge tool true (for pattern f)
   merging f
-  couldn't find merge tool true specified for f
+  couldn't find merge tool true (for pattern f)
   merging f failed!
   0 files updated, 0 files merged, 0 files removed, 1 files unresolved
   use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon
@@ -418,9 +418,9 @@
   true.executable=cat
   # hg update -C 1
   $ hg merge -r 2 --config merge-patterns.f=true --config merge-tools.true.executable=/nonexistent/mergetool
-  couldn't find merge tool true specified for f
+  couldn't find merge tool true (for pattern f)
   merging f
-  couldn't find merge tool true specified for f
+  couldn't find merge tool true (for pattern f)
   merging f failed!
   0 files updated, 0 files merged, 0 files removed, 1 files unresolved
   use 'hg resolve' to retry unresolved file merges or 'hg update -C .' to abandon