I had a quick look via a site-local google search for "hl=' which returned some localized links in answers & questions (to Google services). All in all 57 results.
What's the policy for those links?
Plus: Is it OK to manually edit all those occurrences or will I upset the reviewers when I do this? Should I wait until I gain enough reputation so that I won't?
The site is in English of course but there may be international visitors who'd like to view the linked content in its localized version. Nothing will change or be broken for English readers if the hl=en (or hl=en_us,...) is removed.
Some samples:
http://support.google.com/picasa/bin/answer.py?hl=de&answer=55851 (English)
http://support.google.com/picasa/bin/answer.py?hl=en&answer=55851 (German)
http://support.google.com/picasa/bin/answer.py?answer=55851 (defined by browser/system setting)
https://play.google.com/store/apps/details?id=com.google.android.apps.maps&hl=hu