Thank you for getting back to me.
Do you have any custom code relating to localization? Probably some code in Global.asax file and you have replaced the Global.asax with the one in upgrade patch. I have upgraded a couple of localized projects from Sitefinity 3.7 SP1 to Sitefinity 3.7 SP2 and the localization was working fine. Can you make sure all assemblies in bin directory got replaced properly.
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