It might be hidden by your Content Browser view settings. Make sure that “View Options” → “Show Localized Assets” is selected.
If it’s still missing after that then you can just create it, since we don’t make it by default. 4.13+ also has an “Asset Localization” content menu option that lets you create a placeholder localized asset for your source asset (note that it just copies the source asset to the correct location within the L10N folder).