To reproduce: run the dx-core-webapp (NOT dx-demo-webapp), create a segment in Segments app, then create a page in Pages app using the "basic template", then create a variant and assign the segment you created as the audience. Look in the JCR and navigate to this variant node. Select "display all system properties". Find mgnl:assignedSegment and title properties. See attached screenshot for example.

Properties "mgnl:assignedSegment" and page "title" are being saved with a locale at the end.
If an i18n node is configured AND enabled inside of the site module configuration or the fallback site definition, then this issue doesn't seem to occur.

You can also see this issue on the demo site for the Sportstation site, which has i18n disabled in the site definition by default. If i18n is enabled, the issue goes away.
https://demoauthor.magnolia-cms.com/

Notes from grooming:

• likely issue only in segmentation project confirmed in website too
• LocaleContext population logic