Using the per-revision bisect providing the bisect results,
Good build: 55.0.2867.0 (Revision: 419930).
Bad build: 55.0.2868.0 (Revision: 420217).

You are probably looking for a change made after 420248 (known good), but no later than 420249 (first known bad).
CHANGELOG URL:
The script might not always return single CL as suspectas some perf builds might get missing due to failure.
 https://chromium.googlesource.com/chromium/src/+log/2064859d41bd8d4700807a7f13df6712101586a4..c3b245a46107e57dd0ef8ace954adf648a900ab4

From the CL above, assigning the issue to the concern owner --
@michaelpg -- Could you please look into the issue, pardon me if it has nothing to do with your changes and if possible please assign it to concern owner.

Adding RB Label as this is a recent Regression. Please remove if not required.
Thank You.

Note:1. Unable to check issue on Linux OS as build is not available.
     2. Issue is not reproducible on Mac OS.

michaelpg@: Could you please take a look at this. Cc'ing stevenjb@ as well for more inputs.

Friendly ping to get an update on this issue. There is no 'Relaunch' button seen on Linux Ubuntu 14.04, chrome version:55.0.2875.0.

Please review the blocker label and update this thread as probable M-55 branch date is due for next week or so.

This bug is reported as M55 Beta blocker.Please try to resolve this before M55 branch on Oct 6th,2016 so it has enough baking time in Dev.

Removing the Beta blocker and punting this to Stable blocker for M-55.

michaelpg@/stevenjb@: Please update the blocker label if you feel this should not be blocking and update accordingly as per C#5.

able to reproduce the issue on windows 7 using chrome latest chrome version 56.0.2888.0.
could any one please look into this issue.

michaelpg@ Can we know what's the status of the fix,since we are about to promote M55 to Beta and we need to get the fix into branch soon which on 19th-oct.

MD Settings bugs are never branch blockers, please do not mark them as such. chrome://md-settings is not used by default without a flag being set.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4cb2126002cd187035ba90ee13ebda77e16d81f6

commit 4cb2126002cd187035ba90ee13ebda77e16d81f6
Author: michaelpg <michaelpg@chromium.org>
Date: Wed Dec 14 02:46:48 2016

Language settings: Fix Restart and Remove buttons shown at wrong times

Language settings makes the faulty assumption that the app locale
(navigator.language) will match the the preferred app locale (intl.app_locale).

For some languages, we map a language code to a different locale. For example,
en-ZA is mapped to en-GB when getting the application locale, so the preference
won't match the actual locale used. See l10n_util::CheckAndResolveLocale for
other wacky examples.

Stop using navigator.language when the intl.app_locale pref is available. Also
move more logic into the model and stop checking intl.app_locale in the UI.
Use a more defensive check for the Restart button: show if the locale preference
has changed from its initial value.

BUG= 561227 , 649588 , 633661 
R=stevenjb@chromium.org
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:closure_compilation

Review-Url: https://codereview.chromium.org/2573643005
Cr-Commit-Position: refs/heads/master@{#438403}

[modify] https://crrev.com/4cb2126002cd187035ba90ee13ebda77e16d81f6/chrome/browser/resources/settings/languages_page/languages.js
[modify] https://crrev.com/4cb2126002cd187035ba90ee13ebda77e16d81f6/chrome/browser/resources/settings/languages_page/languages_page.html
[modify] https://crrev.com/4cb2126002cd187035ba90ee13ebda77e16d81f6/chrome/browser/resources/settings/languages_page/languages_page.js
[modify] https://crrev.com/4cb2126002cd187035ba90ee13ebda77e16d81f6/chrome/browser/resources/settings/languages_page/languages_types.js
[modify] https://crrev.com/4cb2126002cd187035ba90ee13ebda77e16d81f6/chrome/browser/ui/webui/settings/languages_handler.cc
[modify] https://crrev.com/4cb2126002cd187035ba90ee13ebda77e16d81f6/chrome/browser/ui/webui/settings/languages_handler.h
[modify] https://crrev.com/4cb2126002cd187035ba90ee13ebda77e16d81f6/chrome/test/data/webui/settings/languages_tests.js