Check your xml-files to ensure that this isnt already covered by the localizationfiles in your project. Most likely, your FileXmlLocalizationProvider is broken, and thats why your reinstall solves the problem. Make sure your episerver.framework file contains the following;
<localization fallbackBehavior="Echo, MissingMessage, FallbackCulture" fallbackCulture="en">
<providers>
<add virtualPath="~/Your/Path/To/Translations" name="languageFiles" type="EPiServer.Framework.Localization.XmlResources.FileXmlLocalizationProvider, EPiServer.Framework" />
</providers>