New option value validation is too tight for languages

CRM-19346 https://github.com/civicrm/civicrm-core/pull/11089 added validation to ensure option values are unique within a group. However, it turns out that languages use the same value for multiple variants & differ on the 'name' field. 

This is a regression of sorts but very obscure & I would be surprised if it will cause any problems. We hit this in our test suite. There are theoretical ways we could hit it live but I don't know if they would ever occur or not if we deployed unpatched